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Texas Guide to Rainwater Harvesting - 2005

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This chapter describes the basic components of a rainwater harvesting system, including the catchment surface, gutters and downspouts, leaf screens, first-flush diverters, roof washers, storage tanks, pressure tanks and pumps, and treatment equipment. It also notes that local codes should be consulted for potable systems.

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The Texas Manual on Rainwater Harvesting Texas Water Development Board Third Edition
The Texas Manual on Rainwater Harvesting Texas Water Development Board in cooperation with Chris Brown Consulting Jan Gerston Consulting Stephen Colley/Architecture Dr. Hari J. Krishna, P.E., Contract Manager Third Edition 2005 Austin, Texas
Acknowledgments The authors would like to thank the following persons for their assistance with the production of this guide: Dr. Hari Krishna, Contract Manager, Texas Water Development Board, and President, American Rainwater Catchment Systems Association (ARCSA); Jen and Paul Radlet, Save the Rain; Richard Heinichen, Tank Town; John Kight, Kendall County Commissioner and Save the Rain board member; Katherine Crawford, Golden Eagle Landscapes; Carolyn Hall, Timbertanks; Dr. Howard Blatt, Feather & Fur Animal Hospital; Dan Wilcox, Advanced Micro Devices; Ron Kreykes, ARCSA board member; Dan Pomerening and Mary Dunford, Bexar County; Billy Kniffen, Menard County Cooperative Extension; Javier Hernandez, Edwards Aquifer Authority; Lara Stuart, CBC; Wendi Kimura, CBC. We also acknowledge the authors of the previous edition of this publication, The Texas Guide to Rainwater Harvesting, Gail Vittori and Wendy Price Todd, AIA. Disclaimer The use of brand names in this publication does not indicate an endorsement by the Texas Water Development Board, or the State of Texas, or any other entity. Views expressed in this report are of the authors and do not necessarily reflect the views of the Texas Water Development Board, or any other entity.
Table of Contents Chapter 1 Introduction..................................................................................................... 1 Chapter 2 Rainwater Harvesting System Components................................................. 5 Basic Components .......................................................................................................... 5 The Catchment Surface................................................................................................... 5 Gutters and Downspouts ................................................................................................. 6 Leaf Screens.................................................................................................................... 7 First-Flush Diverters ....................................................................................................... 8 Roof Washers................................................................................................................ 10 Storage Tanks................................................................................................................ 10 Pressure Tanks and Pumps............................................................................................ 16 Treatment and Disinfection Equipment ........................................................................ 17 Chapter 3 Water Quality and Treatment..................................................................... 21 Considerations for the Rainwater Harvesting System Owner ...................................... 21 Water Quality Standards ............................................................................................... 22 Factors Affecting Water Quality................................................................................... 22 Water Treatment ........................................................................................................... 23 Chapter 4 Water Balance and System Sizing............................................................... 29 How Much Water Can Be Captured? ........................................................................... 29 Rainfall Distribution ..................................................................................................... 30 Calculating Storage Capacity........................................................................................ 32 The Water Balance Method Using Monthly Demand and Supply ............................... 32 Estimating Demand....................................................................................................... 33 Estimating indoor water demand .............................................................................. 33 Indoor water conservation......................................................................................... 35 Estimating outdoor water demand ............................................................................ 36 Chapter 5 Rainwater Harvesting Guidelines ............................................................... 41 RWH Best Management Practices................................................................................ 41 Water Conservation Implementation Task Force Guidelines................................... 41 American Rainwater Catchment Systems Association............................................. 41 Building Codes.............................................................................................................. 41 Cistern Design, Construction, and Capacity ................................................................. 42 Backflow Prevention and Dual-Use Systems ............................................................... 42 Required Rainwater Harvesting Systems...................................................................... 43 Chapter 6 Cost Estimation............................................................................................. 45 Comparing to Other Sources of Water.......................................................................... 51 i
Chapter 7 Financial and Other Incentives ................................................................... 53 Tax Exemptions ............................................................................................................ 53 Municipal Incentives..................................................................................................... 54 Rainwater Harvesting at State Facilities ....................................................................... 55 Performance Contracting .............................................................................................. 56 Appendix A References ................................................................................................. A1 Appendix B Rainfall Data ............................................................................................. A7 Appendix C Case Studies ............................................................................................ A11 Appendix D Tax Exemption Application Form ........................................................ A25 ii
Chapter 1 Introduction Rainwater harvesting is an ancient extending their use; rainwater technique enjoying a revival in eliminates the need for a water popularity due to the inherent quality of softener and the salts added during rainwater and interest in reducing the softening process. consumption of treated water. Rainwater is sodium-free, important Rainwater is valued for its purity and for persons on low-sodium diets. softness. It has a nearly neutral pH, and Rainwater is superior for landscape is free from disinfection by-products, irrigation. salts, minerals, and other natural and man-made contaminants. Plants thrive Rainwater harvesting reduces flow to under irrigation with stored rainwater. stormwater drains and also reduces Appliances last longer when free from non-point source pollution. the corrosive or scale effects of hard Rainwater harvesting helps utilities water. Users with potable systems prefer reduce the summer demand peak and the superior taste and cleansing delay expansion of existing water properties of rainwater. treatment plants. Archeological evidence attests to the Rainwater harvesting reduces capture of rainwater as far back as 4,000 consumers’ utility bills. years ago, and the concept of rainwater Perhaps one of the most interesting harvesting in China may date back 6,000 aspects of rainwater harvesting is years. Ruins of cisterns built as early as learning about the methods of capture, 2000 B.C. for storing runoff from storage, and use of this natural resource hillsides for agricultural and domestic at the place it occurs. This natural purposes are still standing in Israel synergy excludes at least a portion of (Gould and Nissen-Petersen, 1999). water use from the water distribution Advantages and benefits of rainwater infrastructure: the centralized treatment harvesting are numerous (Krishna, facility, storage structures, pumps, 2003). mains, and laterals. The water is free; the only cost is for Rainwater harvesting also includes land- collection and use. based systems with man-made landscape The end use of harvested water is features to channel and concentrate located close to the source, rainwater in either storage basins or eliminating the need for complex and planted areas. costly distribution systems. When assessing the health risks of Rainwater provides a water source drinking rainwater, consider the path when groundwater is unacceptable or taken by the raindrop through a unavailable, or it can augment limited watershed into a reservoir, through groundwater supplies. public drinking water treatment and distribution systems to the end user. The zero hardness of rainwater helps Being the universal solvent, water prevent scale on appliances, absorbs contaminants and minerals on its 1
travels to the reservoir. While in of rainwater. The scope, method, residence in the reservoir, the water can technologies, system complexity, come in contact with all kinds of foreign purpose, and end uses vary from rain materials: oil, animal wastes, chemical barrels for garden irrigation in urban and pharmaceutical wastes, organic areas, to large-scale collection of compounds, industrial outflows, and rainwater for all domestic uses. Some trash. It is the job of the water treatment examples are summarized below: plant to remove harmful contaminants For supplemental irrigation water, the and to kill pathogens. Unfortunately, Wells Branch Municipal Utility when chlorine is used for disinfection, it District in North Austin captures also degrades into disinfection by- rainwater, along with air conditioning products, notably trihalomethanes, condensate, from a new 10,000- which may pose health risks. In contrast, square-foot recreation center into a the raindrop harvested on site will travel 37,000-gallon tank to serve as down a roof via a gutter to a storage irrigation water for a 12-acre tank. Before it can be used for drinking, municipal park with soccer fields and it will be treated by a relatively simple offices. process with equipment that occupies about 9 cubic feet of space. The Lady Bird Johnson Wildflower Research Center in Austin, Texas, Rainwater harvesting can reduce the harvests 300,000 gallons of rainwater volume of storm water, thereby annually from almost 19,000 square lessening the impact on erosion and feet of roof collection area for decreasing the load on storm sewers. irrigation of its native plant Decreasing storm water volume also landscapes. A 6,000-gallon stone helps keep potential storm water cistern and its arching stone aqueduct pollutants, such as pesticides, fertilizers, form the distinctive entry to the and petroleum products, out of rivers research center. and groundwater. The Advanced Micro Devices But along with the independence of semiconductor fabrication plant in rainwater harvesting systems comes the Austin, Texas, does not use utility- inherent responsibility of operation and supplied water for irrigation, saving maintenance. For all systems, this $1.5 million per year by relying on responsibility includes purging the first- captured rainwater and collected flush system, regularly cleaning roof groundwater. washers and tanks, maintaining pumps, and filtering water. For potable systems, Reynolds Metals in Ingleside, Texas, responsibilities include all of the above, uses stormwater captured in and the owner must replace cartridge containment basins as process water filters and maintain disinfection in its metal-processing plant, greatly equipment on schedule, arrange to have offsetting the volume of purchased water tested, and monitor tank levels. water. Rainwater used for drinking should be The city of Columbia, Nuevo León, tested, at a minimum, for pathogens. Mexico, is in the planning stages of Rainwater harvesting, in its essence, is developing rainwater as the basis for the collection, conveyance, and storage the city’s water supply for new 2
growth areas, with large industrial In fact, rainwater harvesting is developments being plumbed for encouraged by Austin and San Antonio storage and catchment. water utilities as a means of conserving On small volcanic or coral islands, water. The State of Texas also offers rainwater harvesting is often the only financial incentives for rainwater option for public water supply, as harvesting systems. Senate Bill 2 of the watersheds are too small to create a 77th Legislature exempts rainwater major river, and groundwater is either harvesting equipment from sales tax, and nonexistent or contaminated with salt allows local governments to exempt water. Bermuda, the U.S. Virgin rainwater harvesting systems from ad Islands, and other Caribbean islands valorem (property) taxes. require cisterns to be included with all Rainwater harvesting systems can be as new construction. simple as a rain barrel for garden In Central Texas, more than 400 full- irrigation at the end of a downspout, or scale rainwater harvesting systems have as complex as a domestic potable system been installed by professional or a multiple end-use system at a large companies, and more than 6,000 rain corporate campus. barrels have been installed through the Rainwater harvesting is practical only City of Austin’s incentive program in the when the volume and frequency of past decade. Countless “do-it- rainfall and size of the catchment surface yourselfers” have installed systems over can generate sufficient water for the the same time period. intended purpose. An estimated 100,000 residential From a financial perspective, the rainwater harvesting systems are in use installation and maintenance costs of a in the United States and its territories rainwater harvesting system for potable (Lye, 2002). More are being installed by water cannot compete with water the urban home gardener seeking supplied by a central utility, but is often healthier plants, the weekend cabin cost-competitive with installation of a owner, and the homeowner intent upon well in rural settings. the “green” building practices – all With a very large catchment surface, seeking a sustainable, high-quality water such as that of big commercial building, source. Rainwater harvesting is also the volume of rainwater, when captured recognized as an important water- and stored, can cost-effectively serve conserving measure, and is best several end uses, such as landscape implemented in conjunction with other irrigation and toilet flushing. efficiency measures in and outside of the home. Some commercial and industrial buildings augment rainwater with Harvested rainwater may also help some condensate from air conditioning Texas communities close the gap systems. During hot, humid months, between supply and demand projected warm, moisture-laden air passing over by the Texas Water Development Board the cooling coils of a residential air (TWDB), as the state’s population nearly conditioner can produce 10 or more doubles between 2000 and 2050 (Texas gallons per day of water. Industrial Water Development Board, 2002). facilities produce thousands of gallons 3
per day of condensate. An advantage of References condensate capture is that its maximum Gould J, Nissen-Petersen E. 1999. production occurs during the hottest Rainwater catchment systems for month of the year, when irrigation need domestic rain: design construction is greatest. Most systems pipe and implementation. London: condensate into the rainwater cistern for Intermediate Technology storage. Publications. 335 p. The depletion of groundwater sources, Krishna H. 2003. An overview of the poor quality of some groundwater, rainwater harvesting systems and high tap fees for isolated properties, the guidelines in the United States. flexibility of rainwater harvesting Proceedings of the First American systems, and modern methods of Rainwater Harvesting Conference; treatment provide excellent reasons to 2003 Aug 21-23; Austin (TX). harvest rainwater for domestic use. Lye D. 2002. Health risks associated The scope of this manual is to serve as a with consumption of untreated water primer in the basics of residential and from household roof catchment small-scale commercial rainwater systems. Journal of the American harvesting systems design. It is intended Water Resources Association to serve as a first step in thinking about 38(5):1301-1306. options for implementing rainwater harvesting systems, as well as Texas Water Development Board. 2002. advantages and constraints. Water for Texas – 2002. Austin (TX): Texas Water Development Board. 155 p. 4
Chapter 2 Rainwater Harvesting System Components Rainwater harvesting is the capture, building code officer should be diversion, and storage of rainwater for a consulted concerning safe, sanitary number of different purposes including operations and construction of these landscape irrigation, drinking and systems. domestic use, aquifer recharge, and stormwater abatement. Basic Components In a residential or small-scale Regardless of the complexity of the application, rainwater harvesting can be system, the domestic rainwater as simple as channeling rain running off harvesting system (Figure 2-1) an unguttered roof to a planted landscape comprises six basic components: area via contoured landscape. To prevent Catchment surface: the collection erosion on sloped surfaces, a bermed surface from which rainfall runs off concave holding area down slope can Gutters and downspouts: channel store water for direct use by turfgrass or water from the roof to the tank plants (Waterfall, 1998). More complex systems include gutters, pipes, storage Leaf screens, first-flush diverters, and tanks or cisterns, filtering, pump(s), and roof washers: components which water treatment for potable use. remove debris and dust from the captured rainwater before it goes to This chapter focuses on residential or the tank small-scale commercial systems, for both irrigation and potable use. One or more storage tanks, also called cisterns The local health department and city Delivery system: gravity-fed or pumped to the end use Treatment/purification: for potable systems, filters and other methods to make the water safe to drink The Catchment Surface The roof of a building or house is the obvious first choice for catchment. For additional capacity, an open-sided barn – called a rain barn or pole barn – can be built. Water tanks and other rainwater system equipment, such as pumps and filters, as well as vehicles, bicycles, and gardening tools, can be stored under the barn. Water quality from different roof Figure 2-1. Typical rainwater harvesting catchments is a function of the type of installation roof material, climatic conditions, and 5
the surrounding environment harvested is usually suitable only for (Vasudevan, 2002). irrigation due to leaching of compounds. Metal Slate. Slate’s smoothness makes it ideal The quantity of rainwater that can be for a catchment surface for potable use, collected from a roof is in part a function assuming no toxic sealant is used; of the roof texture: the smoother the however, cost considerations may better. A commonly used roofing preclude its use. material for rainwater harvesting is sold under the trade name Galvalume®, a 55 Gutters and Downspouts percent aluminum/45 percent zinc alloy- Gutters are installed to capture rainwater coated sheet steel. Galvalume® is also running off the eaves of a building. available with a baked enamel coating, Some gutter installers can provide or it can be painted with epoxy paint. continuous or seamless gutters. Some caution should be exercised For potable water systems, lead cannot regarding roof components. Roofs with be used as gutter solder, as is sometimes copper flashings can cause discoloration the case in older metal gutters. The of porcelain fixtures. slightly acidic quality of rain could dissolve lead and thus contaminate the Clay/concrete tile water supply. Clay and concrete tiles are both porous. The most common materials for gutters Easily available materials are suitable and downspouts are half-round PVC, for potable or nonpotable systems, but vinyl, pipe, seamless aluminum, and may contribute to as much as a 10- galvanized steel. percent loss due to texture, inefficient flow, or evaporation. To reduce water Seamless aluminum gutters are usually loss, tiles can be painted or coated with a installed by professionals, and, therefore, sealant. There is some chance of toxins are more expensive than other options. leaching from the tile sealant or paint, Regardless of material, other necessary but this roof surface is safer when components in addition to the horizontal painted with a special sealant or paint to gutters are the drop outlet, which routes prevent bacterial growth on porous water from the gutters downward and at materials. least two 45-degree elbows which allow Composite or asphalt shingle the downspout pipe to snug to the side of Due to leaching of toxins, composite the house. Additional components shingles are not appropriate for potable include the hardware, brackets, and systems, but can be used to collect water straps to fasten the gutters and for irrigation. Composite roofs have an downspout to the fascia and the wall. approximated 10-percent loss due to Gutter Sizing and Installation inefficient flow or evaporation (Radlet When using the roof of a house as a and Radlet, 2004). catchment surface, it is important to Others consider that many roofs consist of one Wood shingle, tar, and gravel. These or more roof “valleys.” A roof valley roofing materials are rare, and the water occurs where two roof planes meet. This is most common and easy to visualize 6
when considering a house plan with an both before and after the storage tank. “L” or “T” configuration. A roof valley The defense in keeping debris out of a concentrates rainfall runoff from two rainwater harvesting system is some type roof planes before the collected rain of leaf screen along the gutter or in the reaches a gutter. Depending on the size downspout. of roof areas terminating in a roof valley, Depending upon the amount and type of the slope of the roofs, and the intensity tree litter and dust accumulation, the of rainfall, the portion of gutter located homeowner may have to experiment to where the valley water leaves the eave of find the method that works best. Leaf the roof may not be able to capture all screens must be regularly cleaned to be the water at that point, resulting in effective. If not maintained, leaf screens spillage or overrunning. can become clogged and prevent Besides the presence of one or more roof rainwater from flowing into a tank. valleys, other factors that may result in Built-up debris can also harbor bacteria overrunning of gutters include an and the products of leaf decay. inadequate number of downspouts, Leaf guards are usually ¼-inch mesh excessively long roof distances from screens in wire frames that fit along the ridge to eave, steep roof slopes, and length of the gutter. Leaf guards/screens inadequate gutter maintenance. are usually necessary only in locations Variables such as these make any gutter with tree overhang. Guards with profiles sizing rules of thumb difficult to apply. conducive to allowing leaf litter to slide Consult you gutter supplier about your off are also available. situation with special attention to determine where gutter overrunning The funnel-type downspout filter is areas may occur. At these points along made of PVC or galvanized steel fitted an eave, apply strategies to minimize with a stainless steel or brass screen. possible overrunning to improve This type of filter offers the advantage of catchment efficiency. Preventative easy accessibility for cleaning. The strategies may include modifications to funnel is cut into the downspout pipe at the size and configuration of gutters and the same height or slightly higher than addition of gutter boxes with the highest water level in the storage downspouts and roof diverters near the tank. eave edge. Strainer baskets are spherical cage-like Gutters should be installed with slope strainers that slip into the drop outlet of towards the downspout; also the outside the downspout. face of the gutter should be lower than A cylinder of rolled screen inserted into the inside face to encourage drainage the drop outlet serves as another method away from the building wall. of filtering debris. The homeowner may need to experiment with various grid Leaf Screens sizes, from insect screen to hardware To remove debris that gathers on the cloth. catchment surface, and ensure high quality water for either potable use or to Filter socks of nylon mesh can be work well without clogging irrigation installed on the PVC pipe at the tank emitters, a series of filters are necessary. inflow. Essentially, mesh screens remove debris 7
First-Flush Diverters A preliminary study by Rain Water A roof can be a natural collection Harvesting and Waste Water Systems surface for dust, leaves, blooms, twigs, Pty Ltd., a rainwater harvesting insect bodies, animal feces, pesticides, component vendor in Australia, and other airborne residues. The first- recommends that between 13 and 49 flush diverter routes the first flow of gallons be diverted per 1,000 square feet. water from the catchment surface away The primary reason for the wide from the storage tank. The flushed water variation in estimates is that there is no can be routed to a planted area. While exact calculation to determine how much leaf screens remove the larger debris, initial water needs to be diverted because such as leaves, twigs, and blooms that there are many variables that would fall on the roof, the first-flush diverter determine the effectiveness of washing gives the system a chance to rid itself of the contaminants off the collection the smaller contaminants, such as dust, surface, just as there are many variables pollen, and bird and rodent feces. determining the make up of the The simplest first-flush diverter is a PVC contaminants themselves. For example, standpipe (Figure 2-2). The standpipe the slope and smoothness of the fills with water first during a rainfall collection surface, the intensity of the event; the balance of water is routed to rain event, the length of time between the tank. The standpipe is drained events (which adds to the amount of continuously via a pinhole or by leaving accumulated contaminants), and the the screw closure slightly loose. In any nature of the contaminants themselves case, cleaning of the standpipe is add to the difficulty of determining just accomplished by removing the PVC how much rain should be diverted during cover with a wrench and removing first flush. In order to effectively wash a collected debris after each rainfall event. collection surface, a rain intensity of one-tenth of an inch of rain per hour is There are several other types of first- needed to wash a sloped roof. A flat or flush diverters. The ball valve type near-flat collection surface requires 0.18 consists of a floating ball that seals off inches of rain per hour for an effective the top of the diverter pipe (Figure 2-3) washing of the surface. when the pipe files with water. The recommended diversion of first Opinions vary on the volume of flush ranges from one to two gallons of rainwater to divert. The number of dry first-flush diversion for each 100 square days, amount of debris, and roof surface feet of collection area. If using a roof for are all variables to consider. a collection area that drains into gutters, One rule of thumb for first-flush calculate the amount of rainfall area that diversion is to divert a minimum of 10 will be drained into every gutter feeding gallons for every 1,000 square feet of your system. Remember to calculate the collection surface. However, first-flush horizontal equivalent of the “roof volumes vary with the amount of dust on footprint” when calculating your the roof surface, which is a function of catchment area. (Please refer to the the number of dry days, the amount and Figure 4-1 in Chapter 4, Water Balance type of debris, tree overhang, and and System Sizing.) If a gutter receives season. the quantity of runoff that require multiple downspouts, first-flush 8
First-Flush Diverters Standpipe The simplest first-flush diverter is a 6- or 8-inch PVC standpipe (Figure 2-2). The diverter fills with water first, backs up, and then allows water to flow into the main collection piping. These standpipes usually have a cleanout fitting at the bottom, and must be emptied and cleaned out after each rainfall event. The water from the standpipe may be routed to a planted area. A pinhole drilled at the bottom of the pipe or a hose bibb fixture left slightly open (shown) allows water to gradually leak out. If you are using 3” diameter PVC or similar pipe, allow 33” length of pipe per gallon; 4” diameter pipe needs only 18” of length per gallon; and a little over 8” of 6” diameter pipe is needed to catch a gallon of water. Figure 2-2. Standpipe first-flush diverter Standpipe with ball valve The standpipe with ball valve is a variation of the standpipe filter. The cutaway drawing (Figure 2-3) shows the ball valve. As the chamber fills, the ball floats up and seals on the seat, trapping first-flush water and routing the balance of the water to the tank. Figure 2-3. Standpipe with ball valve 9
diversion devices will be required for (handling rainwater from 1,500- and each downspout. 3,500-square-foot catchments, respectively). The box is placed atop a Roof Washers ladder-like stand beside the tank, from The roof washer, placed just ahead of the which the system owner accesses the storage tank, filters small debris for box for cleaning via the ladder. In potable systems and also for systems locations with limited drop, a filter with using drip irrigation. Roof washers the canisters oriented horizontally is consist of a tank, usually between 30- indicated, with the inlet and outlet of the and 50-gallon capacity, with leaf filter being nearly parallel. strainers and a filter (Figure 2-4). One commercially available roof washer has Storage Tanks a 30-micron filter. (A micron, also called The storage tank is the most expensive a micrometer, is one-millionth of a component of the rainwater harvesting meter. A 30-micron filter has pores system. about one-third the diameter of a human The size of storage tank or cistern is hair.) dictated by several variables: the All roof washers must be cleaned. rainwater supply (local precipitation), Without proper maintenance they not the demand, the projected length of dry only become clogged and restrict the spells without rain, the catchment flow of rainwater, but may themselves surface area, aesthetics, personal become breeding grounds for pathogens. preference, and budget. The box roof washer (Figure 2-4) is a A myriad of variations on storage tanks commercially available component and cisterns have been used over the consisting of a fiberglass box with one centuries and in different geographical or two 30-micron canister filters regions: earthenware cisterns in pre- biblical times, large pottery containers in Africa, above-ground vinyl-lined swimming pools in Hawaii, concrete or brick cisterns in the central United States, and, common to old homesteads in Texas, galvanized steel tanks and attractive site-built stone-and-mortar cisterns. For purposes of practicality, this manual will focus on the most common, easily installed, and readily available storage options in Texas, some still functional after a century of use. Storage tank basics Storage tanks must be opaque, either upon purchase or painted later, to Figure 2-4. Box roof washer inhibit algae growth. 10
For potable systems, storage tanks truck, preferably near a driveway or must never have been used to store roadway. toxic materials. Water weighs just over 8 pounds per Tanks must be covered and vents gallon, so even a relatively small 1,500- screened to discourage mosquito gallon tank will weigh 12,400 pounds. A breeding. leaning tank may collapse; therefore, Tanks used for potable systems must tanks should be placed on a stable, level be accessible for cleaning. pad. If the bed consists of a stable substrate, such as caliche, a load of sand Storage tank siting or pea gravel covering the bed may be Tanks should be located as close to sufficient preparation. In some areas, supply and demand points as possible to sand or pea gravel over well-compacted reduce the distance water is conveyed. soil may be sufficient for a small tank. Storage tanks should be protected from Otherwise, a concrete pad should be direct sunlight, if possible. To ease the constructed. When the condition of the load on the pump, tanks should be soil is unknown, enlisting the services of placed as high as practicable. Of course, a structural engineer may be in order to the tank inlet must be lower than the ensure the stability of the soil supporting lowest downspout from the catchment the full cistern weight. area. To compensate for friction losses in the trunk line, a difference of a couple Another consideration is protecting the of feet is preferable. When converting pad from being undermined by either from well water, or if using a well normal erosion or from the tank backup, siting the tanks near the well overflow. The tank should be positioned house facilitates the use of existing such that runoff from other parts of the plumbing. property or from the tank overflow will not undermine the pad. The pad or bed Water runoff should not enter septic should be checked after intense rainfall system drainfields, and any tank events. overflow and drainage should be routed so that it does not affect the foundation Fiberglass of the tanks or any other structures Fiberglass tanks (Figure 2-5) are built in (Macomber, 2001). standard capacities from 50 gallons to Texas does not have specific rules 15,000 gallons and in both vertical concerning protection of rainwater systems from possible contamination sources; however, to ensure a safe water supply, underground tanks should be located at least 50 feet away from animal stables or above-ground application of treated wastewater. Also, runoff from tank overflow should not enter septic system drainfields. If supplemental hauled water might be needed, tank placement should also take into Figure 2-5. Two 10,000-gallon fiberglass consideration accessibility by a water tanks 11
cylinder and low-horizontal cylinder Polypropylene tanks do not retain paint configurations. well, so it is necessary to find off-the- shelf tanks manufactured with opaque Fiberglass tanks under 1,000 gallons are plastic. The fittings of these tanks are expensive for their capacity, so aftermarket modifications. Although polypropylene might be preferred. Tanks easy to plumb, the bulkhead fittings for potable use should have a USDA- might be subject to leakage. approved food-grade resin lining and the tank should be opaque to inhibit algae Wood growth. For aesthetic appeal, a wood tank The durability of fiberglass tanks has (Figure 2-7) is often a highly desirable been tested and proven, weathering the choice for urban and suburban rainwater elements for years in Texas oil fields. harvesters. They are easily repaired. Wood tanks, similar to wood water The fittings on fiberglass tanks are an towers at railroad depots, were integral part of the tank, eliminating the historically made of redwood. Modern potential problem of leaking from an wood tanks are usually of pine, cedar, or aftermarket fitting. cypress wrapped with steel tension cables, and lined with plastic. For Polypropylene potable use, a food-grade liner must be Polypropylene tanks (Figure 2-6) are used. commonly sold at farm and ranch supply retailers for all manner of storage uses. Standard tanks must be installed above ground. For buried installation, specially reinforced tanks are necessary to withstand soil expansion and contraction. They are relatively inexpensive and durable, lightweight, and long lasting. Polypropylene tanks are available in capacities from 50 gallons to 10,000 gallons. Figure 2-7. Installation of a 25,000-gallon Timbertank in Central Texas showing the aesthetic appeal of these wooden tanks These tanks are available in capacities from 700 to 37,000 gallons, and are site- built by skilled technicians. They can be dismantled and reassembled at a different location. Figure 2-6. Low-profile 5,000-gallon polypropylene tanks 12
Metal constructed of stacked rings with sealant Galvanized sheet metal tanks (Figure 2- around the joints. Other types of 8) are also an attractive option for the prefabricated concrete tanks include new urban or suburban garden. They are septic tanks, conduit stood on end, and available in sizes from 150 to 2,500 concrete blocks. These tanks are gallons, and are lightweight and easy to fabricated off-site and dropped into relocate. Tanks can be lined for potable place. use. Most tanks are corrugated galvanized steel dipped in hot zinc for Concrete may be prone to cracking and corrosion resistance. They are lined with leaking, especially in underground tanks a food-grade liner, usually polyethylene in clay soil. Leaks can be easily repaired or PVC, or coated on the inside with although the tank may need to be epoxy paint. The paint, which also drained to make the repair. Involving the extends the life of the metal, must be expertise of a structural engineer to FDA- and NSF-approved for potability. determine the size and spacing of reinforcing steel to match the structural loads of a poured-in-place concrete cistern is highly recommended. A product that repairs leaks in concrete tanks, Xypex™, is now also available and approved for potable use. Figure 2-8. Galvanized sheet metal tanks are usually fitted with a food-grade plastic liner. Concrete Concrete tanks are either poured in place or prefabricated (Figure 2-9). They can be constructed above ground or below ground. Poured-in-place tanks can be Figure 2-9. Concrete tank fabricated from stacking rings of concrete integrated into new construction under a patio, or a basement, and their placement One possible advantage of concrete is considered permanent. tanks is a desirable taste imparted to the A type of concrete tank familiar to water by calcium in the concrete being residents of the Texas Hill Country is dissolved by the slightly acidic 13
rainwater. For potable systems, it is Ferrocement structures (Figure 2-10) essential that the interior of the tank be have commonly been used for water plastered with a high-quality material storage construction in developing approved for potable use. countries due to low cost and availability of materials. Small cracks and leaks can Ferrocement easily be repaired with a mixture of Ferrocement is a low-cost steel and cement and water, which is applied mortar composite material. For purposes where wet spots appear on the tank’s of this manual, GuniteTM and ShotcreteTM exterior. Because walls can be as thin as type will be classified as ferrocements. 1 inch, a ferrocement tank uses less Both involve application of the concrete material than concrete tanks, and thus and mortar under pressure from a gun. can be less expensive. As with poured- Gunite, the dry-gun spray method in in-place concrete construction, which the dry mortar is mixed with assistance from a structural engineer is water at the nozzle, is familiar for its use encouraged. in swimming pool construction. Shotcrete uses a similar application, but In-ground polypropylene the mixture is a prepared slurry. Both In-ground tanks are more costly to install methods are cost-effective for larger for two reasons: the cost of excavation storage tanks. Tanks made of Gunite and and the cost of a more heavily reinforced Shotcrete consist of an armature made tank needed if the tank is to be buried from a grid of steel reinforcing rods tied more than 2-feet deep in well-drained together with wire around which is soils. Burying a tank in clay is not placed a wire form with closely spaced recommended because of the layers of mesh, such as expanded metal expansion/contraction cycles of clay lath. A concrete-sand-water mixture is soil. For deeper installation, the walls of applied over the form and allowed to poly tanks must be manufactured thicker cure. It is important to ensure that the and sometimes an interior bracing ferrocement mix does not contain any structure must be added. Tanks are toxic constituents. Some sources buried for aesthetic or space-saving recommend painting above-ground tanks reasons. white to reflect the sun’s rays, reduce Table 2-1 provides some values to assist evaporation, and keep the water cool. in planning an appropriate-sized pad and cistern to meet your water needs and your available space. Many owners of rainwater harvesting systems use multiple smaller tanks in sequence to meet their storage capacity needs. This has the advantage of allowing the owner to empty a tank in order to perform maintenance on one tank at a time without losing all water in storage. A summary of cistern materials, their Figure 2-10. Ferrocement tanks, such as this features, and some words of caution are one, are built in place using a metal armature provided in Table 2-2 to assist the and a sprayed-on cement. prospective harvester in choosing the 14
appropriate cistern type. Prior to making rainwater installer is recommended to your final selection, consulting with an ensure the right choice for your architect, engineer, or professional situation. Table 2-1. Round Cistern Capacity (Gallons) Height (feet) 6-foot Diameter 12-foot Diameter 18-foot Diameter 6 1,269 5,076 11,421 8 1,692 6,768 15,227 10 2,115 8,460 19,034 12 2,538 10,152 22,841 14 2,961 11,844 26,648 16 3,384 13,535 30,455 18 3,807 15,227 34,262 20 4,230 16,919 38,069 Rain barrel barrel to a second barrel. A screen trap at One of the simplest rainwater the water entry point discourages installations, and a practical choice for mosquito breeding. A food-grade plastic urban dwellers, is the 50- to 75-gallon barrel used for bulk liquid storage in drum used as a rain barrel for irrigation restaurants and grocery stores can be of plant beds. Some commercially fitted with a bulkhead fitting and spigot available rain barrels are manufactured for garden watering. Other options with overflow ports linking the primary include a submersible pump or jet pump. 15
Table 2-2. Cistern Types MATERIAL FEATURES CAUTION Plastics Trash cans (20-50 gallon) commercially available; use only new cans inexpensive Fiberglass commercially available; must be sited on smooth, solid, alterable and moveable level footing Polyethylene/polypropylene commercially available; UV-degradable, must be alterable and moveable painted or tinted Metals Steel drums (55-gallon) commercially available; verify prior to use for toxics; alterable and moveable prone to corrosion an rust; Galvanized steel tanks commercially available; possibly corrosion and rust; alterable and moveable must be lined for potable use Concrete and Masonry Ferrocement durable and immoveable potential to crack and fail Stone, concrete block durable and immoveable difficult to maintain Monolithic/Poured-in-place durable and immoveable potential to crack Wood Redwood, fir, cypress attractive, durable, can be expensive disassembled and moved Adapted from Texas Guide to Rainwater Harvesting, Second Edition, Texas Water Development Board, 1997. clothes washers, dishwashers, hot-water- Pressure Tanks and Pumps on-demand water heaters – require 20– The laws of physics and the topography 30 psi for proper operation. Even some of most homesteads usually demand a drip irrigation system need 20 psi for pump and pressure tank between water proper irrigation. Water gains 1 psi of storage and treatment, and the house or pressure for every 2.31 feet of vertical end use. Standard municipal water rise. So for gravity flow through a 1-inch pressure is 40 pounds per square inch pipe at 40 psi, the storage tanks would (psi) to 60 psi. Many home appliances – 16
have to be more than 90 feet above the house. Since this elevation separation is rarely practical or even desirable, two ways to achieve proper household water pressure are (1) a pump, pressure tank, pressure switch, and check valve (familiar to well owners), or (2) an on-demand pump. Pumps are designed to push water rather than to pull it. Therefore, the system should be designed with the pumps at the same level and as close to the storage tanks as possible. Pump systems draw water from the storage tanks, pressurize it, and store it in a pressure tank until needed. The typical pump-and-pressure tank Figure 2-11. Cistern float filter arrangement consists of a ¾- or 1- horsepower pump, usually a shallow flexible hose, draws water through the well jet pump or a multistage centrifugal filter. pump, the check valve, and pressure switch. A one-way check valve between On-demand pump the storage tank and the pump prevents The new on-demand pumps eliminate pressurized water from being returned to the need for a pressure tank. These the tank. The pressure switch regulates pumps combine a pump, motor, operation of the pressure tank. The controller, check valve, and pressure pressure tank, with a typical capacity of tank function all in one unit. They are 40 gallons, maintains pressure self-priming and are built with a check throughout the system. When the valve incorporated into the suction port. pressure tank reaches a preset threshold, Figure 2-12 shows a typical installation the pressure switch cuts off power to the of an on-demand pump and a 5-micron pump. When there is demand from the fiber filter, 3-micron activated charcoal household, the pressure switch detects filter, and an ultraviolet lamp. Unlike the drop in pressure in the tank and conventional pumps, on-demand pumps activates the pump, drawing more water are designed to activate in response to a into the pressure tank. demand, eliminating the need, cost, and space of a pressure tank. In addition, The cistern float filter (Figure 2-11) some on-demand pumps are specifically allows the pump to draw water from the designed to be used with rainwater. storage tank from between 10 and 16 inches below the surface. Water at this Treatment and Disinfection level is cleaner and fresher than water Equipment closer to the bottom of the tank. The device has a 60-micron filter. An For a nonpotable system used for hose external suction pump, connected via a irrigation, if tree overhang is present, leaf screens on gutters and a roof washer 17
diverting 10 gallons for every 1,000 square feet of roof is sufficient. If drip irrigation is planned, however, sediment filtration may be necessary to prevent clogging of emitters. As standards differ, the drip irrigation manufacturer or vendor should be contacted regarding filtering of water. For potable water systems, treatment beyond the leaf screen and roof washer is necessary to remove sediment and disease-causing pathogens from stored water. Treatment generally consists of filtration and disinfection processes in series before distribution to ensure health and safety. Cartridge Filters and Ultraviolet (UV) Light The most popular disinfection array in Figure 2-12. Typical treatment installation of Texas is two in-line sediment filters – an on-demand pump, 5-micron fiber filter, 3- the 5-micron fiber cartridge filter micron activated charcoal filter, and an followed by the 3-micron activated ultraviolet lamp (top). charcoal cartridge filter – followed by ultraviolet light. This disinfection set-up another cartridge. The ultraviolet (UV) is placed after the pressure tank or after light must be rated to accommodate the the on-demand pump. increased flow. It is important to note that cartridge NSF International (National Sanitation filters must be replaced regularly. Foundation) is an independent testing Otherwise, the filters can actually harbor and certification organization. Filter bacteria and their food supply. The 5- performance can be researched using a micron filter mechanically removes simple search feature by model or suspended particles and dust. The 3- manufacturer on the NSF website. (See micron filter mechanically traps References.) It is best to purchase NSF- microscopic particles while smaller certified equipment. organic molecules are absorbed by the Maintenance of the UV light involves activated surface. In theory, activated cleaning of the quartz sleeve. Many UV charcoal can absorb objectionable odors lights are designed with an integral and tastes, and even some protozoa and wiper unit. Manual cleaning of the cysts (Macomber, 2001). sleeve is not recommended due to the Filters can be arrayed in parallel for possibility of breakage. greater water flow. In other words, two UV lamps are rated in gallons per 5-micron fiber filters can be stacked in minute. For single 5-micron and 3- one large cartridge followed by two 3- micron in-line filters, a UV light rated at micron activated charcoal filters in 12 gallons per minute is sufficient. For 18
filters in parallel installation, a UV light water, referred to as “brine,” containing rated for a higher flow is needed. In-line a concentrate of the contaminants flow restrictors can match flow to the filtered from the feed water, is UV light rating. discharged. The amount of reject water, however, is directly proportional to the UV lights must be replaced after a purity of the feed water. Rainwater, as a maximum of 10,000 hours of operation. purer water source to begin with, would Some lights come with alarms warning generate less brine. Reverse osmosis of diminished intensity. membranes must be changed before they Ozone are fouled by contaminants. Chemically, ozone is O3: essentially a Reverse osmosis (RO) equipment for more reactive form of molecular oxygen household use is commercially available made up of three atoms of oxygen. from home improvement stores such as Ozone acts as a powerful oxidizing agent Lowe’s and Home Depot. to reduce color, to eliminate foul odors, and to reduce total organic carbon in Chlorination water. For disinfection purposes, an For those choosing to disinfect with ozone generator forces ozone into chlorine, automatic self-dosing systems storage tanks through rings or a diffuser are available. A chlorine pump injects stone. Ozone is unstable and reacts chlorine into the water as it enters the quickly to revert to O2 and dissipates house. In this system, appropriate through the atmosphere within 15 contact time is critical to kill bacteria. A minutes. practical chlorine contact time is usually from 2 minutes to 5 minutes with a free A rainwater harvesting system owner in chlorine residual of 2 parts per million Fort Worth uses an ozone generator to (ppm). The time length is based on water keep the water in his 25,000 gallons of pH, temperature, and amount of bacteria. storage “fresh” by circulating ozone Contact time increases with pH and through the five tanks at night. A decreases with temperature. K values standard sprinkler controller switches the (contact times) are shown in Table 3-3. ozone feed from tank to tank. Membrane Filtration (Reverse References Osmosis and Nanofiltration) Membrane filtration, such as reverse Macomber P. 2001. Guidelines on osmosis and nanofiltration work by rainwater catchment systems for forcing water under high pressure Hawaii. Manoa (HI): College of through a semipermeable membrane to Tropical Agriculture and Human filter dissolved solids and salts, both of Resources, University of Hawaii at which are in very low concentrations in Manoa. 51 p. rainwater. Membrane processes, NSF International, filter performance, however, have been known empirically www.nsf.org/certified/DWTU/ to produce “sweeter” water, perhaps by filtering out dissolved metals from Radlet J, Radlet P. 2004. Rainwater plumbing. harvesting design and installation workshop. Boerne (TX): Save the A certain amount of feed water is lost in Rain. any membrane filtration process. Reject 19
Rain Water Harvesting and Waste Water collected from rooftops in Bryan and Systems Pty Ltd., College Station, Texas [master www.rainharvesting.com.au thesis]. College Station (TX): Texas A&M University. 180 p. Texas Water Development Board. 1997. Texas guide to rainwater harvesting. Waterfall P. 1998. Harvesting rainwater Austin (TX): Texas Water for landscape use. Tucson (AZ): The Development Board. 58 p. University of Arizona College of Agriculture and Life Sciences. 39 p. Vasudevan L. 2002. A study of biological contaminants in rainwater 20
Chapter 3 Water Quality and Treatment The raindrop as it falls from the cloud is ranges of 100 ppm to more than 800 soft, and is among the cleanest of water ppm. sources. Use of captured rainwater offers The sodium content of some municipal several advantages. water ranges from 10 parts per million Rainwater is sodium-free, a benefit for (ppm) to as high as 250 ppm. Rainwater persons on restricted sodium diets. intended solely for outdoor irrigation may need no treatment at all except for a Irrigation with captured rainwater screen between the catchment surface promotes healthy plant growth. Also, and downspout to keep debris out of the being soft water, rainwater extends the tank, and, if the tank is to supply a drip life of appliances as it does not form irrigation system, a small-pore filter at scale or mineral deposits. the tank outlet to keep emitters from The environment, the catchment surface, clogging. and the storage tanks affect the quality of harvested rainwater. With minimal Considerations for the Rainwater treatment and adequate care of the Harvesting System Owner system, however, rainfall can be used as It is worth noting that owners of potable water, as well as for irrigation. rainwater harvesting systems who supply The falling raindrop acquires slight all domestic needs essentially become acidity as it dissolves carbon dioxide and owners of their “water supply systems,” nitrogen. Contaminants captured by the responsible for routine maintenance, rain from the catchment surface and including filter and lamp replacement, storage tanks are of concern for those leak repair, monitoring of water quality, intending to use rainwater as their and system upgrades. potable water source. The catchment The rainwater harvesting system owner area may have dust, dirt, fecal matter is responsible for both water supply and from birds and small animals, and plant water quality. Maintenance of a debris such as leaves and twigs. rainwater harvesting system is an Rainwater intended for domestic potable ongoing periodic duty, to include: use must be treated using appropriate filtration and disinfection equipment, monitoring tank levels, discussed in Chapter 2, Rainwater cleaning gutters and first-flush Harvesting System Components. devices, repairing leaks, Total dissolved solids (TDS) in repairing and maintaining the system, rainwater, originating from particulate and matter suspended in the atmosphere, adopting efficient water use practices. range from 2 milligrams per liter (mg/l or ppm)1 to 20 mg/l across Texas, compared with municipal water TDS In addition, owners of potable systems must adopt a regimen of: 1 changing out filters regularly, For dilute aqueous solutions mg/l is approximately equal to ppm because a liter of water weighs one kilogram. 21
maintaining disinfection equipment, the state, acid rain is not considered a such as cleaning and replacing serious concern in Texas. ultraviolet lamps, and regularly testing water quality. Particulate matter Particulate matter refers to smoke, dust, Water Quality Standards and soot suspended in the air. Fine No federal or state standards exist particulates can be emitted by industrial currently for harvested rainwater quality, and residential combustion, vehicle although state standards may be exhaust, agricultural controlled burns, developed in 2006. and sandstorms. As rainwater falls through the atmosphere, it can The latest list of drinking water incorporate these contaminants. requirements can be found on the United States Environmental Protection Particulate matter is generally not a Agency’s website. (See References.) The concern for rainwater harvesting in next section discusses the potential Texas. However, if you wish, geographic vectors by which contaminants get into data on particulate matter can be rainwater. For those intending to harvest accessed at the Air Quality Monitoring rainwater for potable use, the web page of the Texas Commission on microbiological contaminants E. coli, Environmental Quality (TCEQ). (See Cryptosporidium, Giardia lamblia, total References.) coliforms, legionella, fecal coliforms, Chemical compounds and viruses, are probably of greatest Information on chemical constituents concern, and rainwater should be tested can also be found on the TCEQ Air to ensure that none of them are found Quality website. (See References.) (Lye, 2002). County health department and city building code staff should also In agricultural areas, rainwater could be consulted concerning safe, sanitary have a higher concentration of nitrates operations and construction of rainwater due to fertilizer residue in the harvesting systems. atmosphere (Thomas and Grenne, 1993). Pesticide residues from crop dusting in Factors Affecting Water Quality agricultural areas may also be present. pH (acidity/alkalinity) Also, dust derived from calcium-rich As a raindrop falls and comes in contact soils in Central and West Texas can add with the atmosphere, it dissolves 1 mg/l to 2 mg/l of hardness to the water. naturally occurring carbon dioxide to Hard water has a high mineral content, form a weak acid. The resultant pH is usually consisting of calcium and about 5.7, whereas a pH of 7.0 is neutral. magnesium in the form of carbonates. (A slight buffering using 1 tablespoon of In industrial areas, rainwater samples baking soda to 100 gallons of water in can have slightly higher values of the tank will neutralize the acid, if suspended solids concentration and desired. Also, a concrete storage tank turbidity due to the greater amount of will impart a slight alkalinity to the particulate matter in the air (Thomas and water.) While Northeast Texas tends to Grenne, 1993). experience an even lower pH (more acidic) rainwater than in other parts of 22
Catchment surface the valve on the linking pipe between When rainwater comes in contact with a tanks. catchment surface, it can wash bacteria, molds, algae, fecal matter, other organic Water Treatment matter, and/or dust into storage tanks. The cleanliness of the roof in a rainwater The longer the span of continuous harvesting system most directly affects number of dry days (days without the quality of the captured water. The rainfall), the more catchment debris is cleaner the roof, the less strain is placed washed off the roof by a rainfall event on the treatment equipment. It is (Thomas and Grenne, 1993; Vasudevan, advisable that overhanging branches be 2002). cut away both to avoid tree litter and to deny access to the roof by rodents and Tanks lizards. The more filtering of rainwater prior to the storage tanks, the less sedimentation For potable systems, a plain galvanized and introduction of organic matter will roof or a metal roof with epoxy or latex occur within the tanks. Gutter screens, paint is recommended. Composite or first-flush diverters, roof washers, and asphalt shingles are not advisable, as other types of pre-tank filters are toxic components can be leached out by discussed in Chapter 2. Sedimentation rainwater. See Chapter 2 for more reduces the capacity of tanks, and the information on roofing material. breakdown of plant and animal matter To improve water quality, several may affect the color and taste of water, treatment methods are discussed. It is the in addition to providing nutrients for responsibility of the individual installer microorganisms. or homeowner to weigh the advantages Most storage tanks are equipped with and disadvantages of each method for manholes to allow access for cleaning. appropriateness for the individual Sediment and sludge can be pumped out situation. A synopsis of treatment or siphoned out using hose with an techniques is shown in Table 3-1. A inverted funnel at one end without discussion of the equipment is included draining the tank annually. in Chapter 2. Multiple linked tanks allow one tank to be taken off line for cleaning by closing 23
Table 3-1. Treatment Techniques METHOD LOCATION RESULT Treatment Screening Leaf screens and strainers gutters and downspouts prevent leaves and other debris from entering tank Settling Sedimentation within tank settles out particulate matter Activated charcoal before tap removes chlorine* Filtering Roof washer before tank eliminates suspended material In-line/multi-cartridge after pump sieves sediment Activated charcoal after sediment filter removes chlorine, improves taste Slow sand separate tank traps particulate matter Microbiological treatment /Disinfection Boiling/distilling before use kills microorganisms Chemical treatments within tank or at pump (Chlorine or Iodine) (liquid, tablet, or granular) kills microorganisms before activated charcoal filter Ultraviolet light after activated charcoal kills microorganisms filter, before tap Ozonation after activated charcoal kills microorganisms filter, before tap Nanofiltration before use; polymer membrane removes molecules -3 -6 (pores 10 to 10 inch ) Reverse osmosis before use: polymer removes ions (contaminants membrane (pores 10-9 inch) and microorganisms) *Should be used if chlorine has been used as a disinfectant. Adapted from Texas Guide to Rainwater Harvesting, Second Edition, Texas Water Development Board, 1997. 24
In either case, it is a good idea to Chlorination carefully dilute the chlorine source in a Chlorination is mentioned here more for bucket of water, and then stir with a its historical value than for practical clean paddle to hasten mixing application. Chlorine has been used to (Macomber, 2001). Chlorine contact disinfect public drinking water since times are show in Table 3-2. 1908, and it is still used extensively by rainwater harvesters in Hawaii, the U.S. The use of chlorine for disinfection Virgin Islands, and in older rainwater presents a few drawbacks. Chlorine harvesting systems in Kentucky and combines with decaying organic matter Ohio. Chlorine must be present in a in water to form trihalomethanes. This concentration of 1 ppm to achieve disinfection by-product has been found disinfection. Liquid chlorine, in the form to cause cancer in laboratory rats. Also, of laundry bleach, usually has 6 percent some users may find the taste and smell available sodium hypochlorite. For of chlorine objectionable. To address disinfection purposes, 2 fluid ounces this concern, an activated carbon filter (¼ cup) must be added per 1,000 gallons may be used to help remove chlorine. of rainwater. Household bleach products, Chlorine does not kill Giardia or however, are not labeled for use in water Cryptosporidium, which are cysts treatment by the Food and Drug protected by their outer shells. Persons Administration. A purer form of with weakened or compromised immune chlorine, which comes in solid form for systems are particularly susceptible to swimming pool disinfection, is calcium these maladies. To filter out Giardia and hypochlorite, usually with 75 percent Cryptosporidum cysts, an absolute 1- available chlorine. At that strength, 0.85 micron filter, certified by the NSF, is ounces by weight in 1,000 gallons of needed (Macomber, 2001). water would result in a level of 1 ppm. Table 3-2. Contact Time with Chlorine Water Water temperature pH 50 F or 45 F 40 F or warmer colder Contact time in minutes 6.0 3 4 5 6.5 4 5 6 7.0 8 10 12 7.5 12 15 18 8.0 16 20 24 UV Light UV light has been used in Europe for common practice in U.S. utilities. disinfection of water since the early Bacteria, virus, and cysts are killed by 1900s, and its use has now become exposure to UV light. The water must go 25
through sediment filtration before the (See References.) The testing fee is ultraviolet light treatment because usually between $15 and $25. pathogens can be shadowed from the UV Homeowners should contact the health light by suspended particles in the water. department prior to sample collection to In water with very high bacterial counts, procure a collection kit and to learn the some bacteria will be shielded by the proper methods for a grab sample or a bodies of other bacteria cells. faucet sample. UV lights are benign: they disinfect Texas Department of State Health without leaving behind any disinfection Services will test for fecal coliforms for by-products. They use minimal power a fee of $20 per sample. (See for operation. One should follow References.) A collection kit can be manufacturer’s recommendations for ordered from TDSHS at (512) 458-7598. replacement of bulbs. Commercial laboratories are listed in Testing telephone Yellow Pages under Harvested rainwater should be tested Laboratories–Analytical & Testing. For before drinking and periodically a fee, the lab will test water for thereafter. Harvested rainwater should pathogens. For an additional fee, labs be tested both before and after treatment will test for other contaminants, such as to ensure treatment is working. It is metals and pesticides. advisable to test water quarterly at a minimum, if used for drinking. References Harvested rainwater can be tested by a Lye D. 2002. Health risks associated commercial analytical laboratory, the with consumption of untreated water county health departments of many from household roof catchment Texas counties, or the Texas Department systems. Journal of the American of Health. Water Resources Association Before capturing rainwater samples for 38(5):1301-1306. testing, contact the testing entity first to Macomber P. 2001. Guidelines on become informed of requirements for rainwater catchment systems for container type and cleanliness, sample Hawaii. Manoa (HI): College of volume, number of samples needed, and Tropical Agriculture and Human time constraints for return of the sample. Resources, University of Hawaii at For instance, for total coliform testing, Manoa. 51 p. water must usually be captured in a Texas Commission on Environmental sterile container issued by the testing Quality, Air Quality Monitoring, entity and returned within a maximum of www.tceq.state.tx.us/nav/data/pm25. 30 to 36 hours. Testing for pH, html performed by commercial analytical laboratories must be done on site; other Texas Commission on Environmental tests are less time-critical. Quality, chemical constituents, www.tnrcc.state.tx.us/airquality.html A list of county health departments that will test for total and fecal coliform can Texas Department of State Health be found on the Texas Department of Services, county health departments, State Health Services (TDSHS) website. 26
www.dshs.state.tx.us/regions/default. United States Environmental Protection shtm Agency, drinking water requirements, www.epa.gov/safewater/mcl.html Texas Department of State Health Services, testing for fecal coliforms, Vasudevan L. 2002. A study of www.dshs.state.tx.us/lab/default.shtm biological contaminants in rainwater collected from rooftops in Bryan and Thomas PR, Grenne GR. 1993. College Station, Texas [masters Rainwater quality from different roof thesis]. College Station (TX): Texas catchments. Water Science A&M University. 90 p. Technology (28):290-99. 27
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Chapter 4 Water Balance and System Sizing The basic rule for sizing any rainwater sufficient. On the other hand, if harvesting system is that the volume of rainwater is intended to be the sole water that can be captured and stored source of water for all indoor and (the supply) must equal or exceed the outdoor domestic end uses, a more volume of water used (the demand). precise reckoning is necessary to ensure adequate supply. The variables of rainfall and water demand determine the relationship How Much Water Can Be between required catchment area and Captured? storage capacity. In some cases, it may be necessary to increase catchment In theory, approximately 0.62 gallons surface area by addition of a rain barn or per square foot of collection surface per outbuilding to capture enough rainwater inch of rainfall can be collected. In to meet demand. Cistern capacity must practice, however, some rainwater is lost be sufficient to store enough water to see to first flush, evaporation, splash-out or the system and its users through the overshoot from the gutters in hard rains, longest expected interval without rain. and possibly leaks. Rough collection surfaces are less efficient at conveying The following sections describe ways to water, as water captured in pore spaces determine the amount of rainfall, the tends to be lost to evaporation. estimated demand, and how much storage capacity is needed to provide an Also impacting achievable efficiency is adequate water supply. the inability of the system to capture all water during intense rainfall events. For Intended End Use instance, if the flow-through capacity of The first decision in rainwater harvesting a filter-type roof washer is exceeded, system design is the intended use of the spillage may occur. Additionally, after water. If rainwater is to be used only for storage tanks are full, rainwater can be irrigation, a rough estimate of demand, lost as overflow. supply, and storage capacity may be Figure 4-1. Catchment areas of three different roofs 29
Figure 4-2. Average annual precipitation in Texas, in inches For planning purposes, therefore, these volume of storage capacity that can be inherent inefficiencies of the system installed. need to be factored into the water supply calculation. Most installers assume an Collection Surface efficiency of 75 percent to 90 percent. The collection surface is the “footprint” of the roof (Figure 4-1). In other words, In most Texas locations, rainfall occurs regardless of the pitch of the roof, the seasonally, requiring a storage capacity effective collection surface is the area sufficient to store water collected during covered by collection surface (length rainy times to last through the dry spells. times width of the roof from eave to In West Texas, total annual rainfall eave and front to rear). Obviously if only might not be sufficient to allow a one side of the structure is guttered, only residence with a moderate-sized the area drained by the gutters is used in collection surface to capture sufficient the calculation. water for all domestic use. Some residences might be constrained by the Rainfall Distribution area of the collection surfaces or the In Texas, average annual rainfall decreases roughly 1 inch every 15 miles, 30
the total available volume of such an event is rarely captured. Another consideration is that most rainfall occurs seasonally; annual rainfall is not evenly distributed throughout the 12 months of the year. The monthly distribution of rainfall is an important factor to consider for sizing a system. Monthly rainfall data for selected Texas cities is given in Appendix B. Monthly Rainfall Figure 4-3. Maximum number of dry days Two different estimators of monthly (Krishna, 2003) rainfall are commonly used: average rainfall and median rainfall. Average as you go from east to west (Figure 4-2), annual rainfall is calculated by taking the from 56 inches per year in Beaumont to sum of historical rainfall and dividing by less than 8 inches per year in El Paso. As the number of years of recorded data. one moves westward across the state, the This information is available from prevalence and severity of droughts must numerous public sources, including the also be considered. National Climate Data Center website. To ensure a year-round water supply, the (See References.) Median rainfall is the catchment area and storage capacity amount of rainfall that occurs in the must be sized to meet water demand midpoint of all historic rainfall totals for through the longest expected interval any given month. In other words, without rain. For instance, in West historically for the month in question, Texas, the historic longest span of half of the time the rainfall was less than continuous dry days has exceeded three the median and half of the time rainfall months. For reference purposes, a was more than the median. Median contour map of historical maximum values and average rainfall values for number of dry days in Texas is shown in representative Texas cities are provided Figure 4-3 (Krishna, 2003). If the in Appendix B. rainwater harvesting system is intended Median rainfall provides for a more to be the sole water source for a conservative calculation of system sizing household, the designer must size the than average rainfall. The median value system to accommodate the longest for rainfall is usually lower than the anticipated time without rain, or average value since large rainfall events otherwise plan for another water source, tend to drive the average value higher. In such as a well backup or hauled water. other words, the sum of monthly Also, rainfall from high-intensity, short- medians is lower than the annual average duration rainfall events may be lost to due to the fact that the arithmetic overflow from storage tanks or splash- average is skewed by high-intensity out from the gutters. Although these rainfall events. For planning purposes, intense rainfall events are considered median monthly rainfall can be used to part of the cumulative annual rainfall, estimate water availability to a 31
reasonable degree of certainty (Krishna, The Water Balance Method Using 2001). Monthly Demand and Supply For example, in the sample calculations One method of determining the at the end of this chapter, the average feasibility of a proposed system is the annual rainfall for Dallas is about 35.0 monthly water balance method. This inches, but the sum of the monthly method of calculation is similar to medians is only 29.3 inches. maintaining a monthly checkbook balance. Starting with an assumed Calculating Storage Capacity volume of water already in the tanks, the Once the median or average potential for volume captured each month is added to rainfall capture is known from rainfall the previous balance and the demand is data and catchment area, it will be subtracted. The initial volume of water necessary to calculate storage capacity. in the tanks would be provided by The decision of whether rainwater will hauling or capturing water prior to be used for irrigation, potable and withdrawing water from the system. An domestic use, or both, will dictate water example is presented at the end of this demand, and therefore, capacity. chapter. A simple method of roughly estimating Data and calculations can be entered on storage capacity popular among an electronic spreadsheet to enable the professional installers is to size the user to compare different variables of storage capacity to meet quarterly catchment area and storage. It is demand. The system is sized to meet suggested that homeowners experiment estimated demand for a three-month with different variables of storage period without rain. Annual estimated capacity and, if applicable, catchment demand is divided by four to yield surface to find individual levels of necessary storage capacity using this comfort and affordability for catchment approach. This approach, however, may size and storage capacity. result in a more expensive system due to As mentioned above: higher storage costs. catchment area and rainfall determine If a rainwater harvesting system is to be supply, and the sole water supply, overbuilding demand dictates required storage ensures a safety margin. As with many capacity. things in life, it helps to hope for the best but plan for the worst. Even when A commitment to conserving water with budget constraints may not allow the water-saving fixtures, appliances, user to install as much storage capacity practices indoors, and low-water-use as a sizing method may indicate, it is landscaping outdoors is an essential important to provide for an area where component of any rainwater harvesting additional tanks or cisterns can be system design. Not only is conservation installed at a later date when finances good stewardship of natural resources, it permit. also reduces the costs for storage capacity and related system components. If the amount of rainwater that can be captured – calculated from roof area and rainfall – is adequate or more than 32
adequate to meet estimated demand, and efficient water use practices both indoors meets the physical constraints of the and outdoors. building design, then storage capacity can be sized to meet estimated demand. Estimating indoor water demand If the monthly amount of water that can Indoor water demand is largely be captured, accounting for dry spells, is unaffected by changes in weather, less than monthly estimated demand, although changes in household then additional catchment area or occupancy rates depending upon seasons supplemental supplies of water (such as and ages of household members, more groundwater from a well) will need to be water use during the hot summer considered. months, and very minor changes in consumption of water due to increases in In drier areas, no matter how large the temperature may be worth factoring in storage capacity, catchment area may some instances. The results of a study of need to be increased with a rain barn or 1,200 single-family homes by the additional roof area to meet demand. American Water Works Association At the end of this chapter, an example of (AWWA) in 1999 found that the average a water balance calculation is shown for water conserving households used the City of Dallas. approximately 49.6 gallons per person per day (American Water Works Estimating Demand Association, 1999). A water-conserving household will use Table 4-1 can be used to calculate indoor between 25 and 50 gallons per person water demand. Many households use per day. (Note that total gallons per less than the average of 49.6 gallons per capita per day figures published for person found in the 1999 report by the municipalities divide all the water AWWA, Residential End Uses of Water. distributed by the population, yielding a The water volumes shown in the table much larger amount per capita than assume a water-conserving household, actual domestic consumption.) with water-conserving fixtures and good Households served previously by a water practices, such as shutting off the water utility can read monthly demand from while brushing teeth or shaving. Overall their meter or water bill to find monthly demand in showers, baths, and faucet demand for purposes of building a new uses is a function of both time of use and rainwater harvesting system. Divide the rate of flow. Many people do not open monthly total by the number of people in the flow rate as high as it could be the house, and the days in the month to finding low or moderate flow rates more get a daily per capita demand number. comfortable. In estimating demand, measuring flow rates and consumption Water conservation is covered later in in the household may be worth the effort this chapter. Households solely to get more accurate estimates. dependent upon rainwater should adopt 33
Table 4-1. Estimating Indoor Daily Domestic Demand A. B. C. D. E. Water Assumptions Adjustments to Number of Household consumption from AWWA assumptions persons in monthly using Residential End- (adjust up or household demand conserving Use Study down according fixtures to actual use) A x (B or C )x D x 30 Toilets (use only appropriate type) ULFT 1.6 gal/flush 6 flushes/ person/day Dual Flush 1 gal/flush 6 flushes/ liquids person/day 1.6 gal/flush solids Baths & showers Showerhead 2.2 gal/min 5 minutes/ person/day Bath 50 gal/bath NA Faucets 2.2 5 minutes/ (personal gal/faucet/min person/day hygiene, cooking, and cleaning of surfaces) Appliances or uses which are measured on a per-use basis (not a per-person basis): Clothes washer 18–25 gal/load 2.6 loads/week Front-loading (horizontal-axis) Dishwasher 8 gal/cycle 0.7 cycles/day Miscellaneous other Total One can use Table 4-1 if the designer patterns. The average values in the prefers to incorporate known or expected second column are offered for behavioral habits into the water demand information, but as with all averages, are estimates. The values in the first column subject to wide variation based upon are to be multiplied by variables actual circumstances. An example is reflecting your own household water use dual flush toilets – multiply three flushes 34
per day liquid only (1 gpf), and add three designed to use 2.2 gallons per minute flushes per day for solids (1.6 gpf), (3x1) at 60 psi, or 2.5 gpm at 80 psi (Table + (3x1.6) = 7.8 gallons multiplied by 3 4-1). Studies have shown that most persons = 23.4 gpd household demand x people feel comfortable at less than 30 days = 702 gallons per month. The full flow rates, so using the new authors recommend verifying any fixtures (which are the only ones sold assumptions against the records of in the United States since 1992) historical use from a municipal water bill should provide you with an efficient if available. and comfortable experience. Indoor water conservation Hot water on demand. These wall- mounted units heat water just prior to Indoor domestic water conservation can use, eliminating the waste of waiting be achieved by a combination of for hot water from the water heater fixtures, appliances, and water- while cold water is allowed to flow conserving practices. The advantage of down the drain. Hot water loop water-conserving appliances is that they systems keep hot water continuously require no change in household routine. circulating to achieve the same goal, Some water-conserving practices need but can use more energy. Another on- user action, such as turning off the water demand unit heats water quickly only while brushing teeth or shaving; washing when activated by a pushbutton, vegetables in a pan rather than under a rather than circulating water through a stream; washing only full loads of loop, saving both water and energy. A laundry and dishes; and keeping a rebate from San Antonio Water pitcher of water in the refrigerator, rather System (SAWS) is available for than waiting for cold water to arrive installation of this type of on-demand from a faucet. circulation system. Water conservation appliances include: Horizontal-axis (front-loading) clothes Ultralow flush toilets (ULFTs). Since washers. Because clothes are tumbled 1993, only ULFTs with 1.6 gallons through a small volume of water in per flush may be sold in the United the bottom of the drum (rather than States. Older toilets should be washed in a full tub of water), this replaced with the more efficient appliance can save up to half the models. Some of the ULFTs require water of a traditional clothes washer. special early closing flappers to It is also as much as 42 percent more maintain their low-flow rates, so care energy efficient. A list of front- should be taken in purchasing the loading, horizontal-axis clothes correct replacement flapper for washers is maintained by the leaking toilets. If purchasing a new Consortium for Energy Efficiency toilet, those that do not use early online. (See References.) Several closure flappers are recommended. municipal utilities in Texas, including Dual-flush toilets (using less volume City of Austin, SAWS, and Bexar for liquid wastes) are also a good Met, offer rebates for the purchase of choice for a water-wise household. these energy- and water-efficient Faucet aerators and efficient appliances. showerheads. These fixtures are 35
Estimating outdoor water demand A recommended general reference for Outdoor water demand peaks in hot, dry water-wise landscaping is Xeriscape: summer. In fact, as much as 60 percent Landscape Water Conservation, of municipal water demand in the publication B-1584, available online. summer is attributable to irrigation. (See References.) Other plant lists and resources are available at the Texas The water demands of a large turfgrass Master Gardeners’ website. (See area almost always preclude the sole use References.) Many municipal water of harvested rainwater for irrigation. utilities, including those in the cites of El Many urban dwellers capture rainwater Paso, Houston, Austin, San Antonio, and for irrigation of vegetable and the Metroplex area have published ornamental gardens. Because it is free of water-wise landscaping information salts and minerals, rainwater promotes tailored to local climate and soil healthy plant growth. In urban areas, conditions rainwater harvesters may reduce their It is recommended that rainwater water bill by substituting harvested harvesting families install landscapes of rainwater for municipal water for garden native and adapted plants, and also irrigation. ascribe to the seven principles of For both the health of landscape plants Xeriscaping. A water-wise landscape and water use-efficiency, the best way to can be quite attractive, while conserving water plants is according to their needs. water and demanding less care than a For most plants adapted to Texas’ garden of non-native or non-adapted climate, water stress is visually evident plants. well before plant death. Signs of water stress include a gray blue tint to leaves, leaf rolling, and in the case of turfgrass, Principles of Water-Wise Landscaping a footprint that does not spring back. Watering infrequently and deeply has 1.Plan and design for water conservation. been shown to promote plant health, waiting until plants need the water helps 2. Create practical turf areas. the water user to be sure that they are 3. Group plants of similar water needs growing a healthy landscape. together. For planning purposes, historical 4. Use soil amendments like compost to evapotranspiration can be used to project allow the soil to retain more water. potential water demands. Evapotranspiration is the term for water 5. Use mulches, especially in high and use by plants, the combination of moderate watering zones, to lessen evaporation from the soil and soil evaporation. transpiration from the plant leaves. An 6. Irrigate efficiently by applying the right estimated value called potential amount of water at the right time. evapotranspiration is available on the Texas Evapotranspiration website, or 7. Maintain the landscape appropriately can be calculated from weather-related by fertilizing, mowing, and pruning. data. (See References.) 36
References Krishna H. 2003. An overview of rainwater harvesting systems and American Water Works Association. guidelines in the United States. 1999. Residential end uses of water. Proceedings of the First American Denver (CO): American Water Rainwater Harvesting Conference; Works Association Research 2003 Aug 21-23; Austin (TX). Foundation. 310 p. National Climate Data Center, Consortium for Energy Efficiency, list of www.ncdc.noaa.gov clothes washers, www.cee1.org/resid/seha/rwsh/rwsh- Texas Evapotranspiration Network, main.php3 texaset.tamu.edu Krishna H. 2001. Rainwater catchment Texas Master Gardeners, systems in Texas. Proceedings of the aggiehorticulture.tamu.edu/mastergd/ 10th International Conference on mg.html Rainwater Catchment Systems of the Xeriscape: Landscape Water International Rainwater Catchments Conservation, publication B-1584, Systems Association; 2001 Sep 10- tcebookstore.org 14; Mannheim, Germany. 37
Rainwater Harvesting System Sizing Sample Water Balance Calculations for Dallas, Texas Two methods of determining system sizing are shown below. In the first example, monthly average rainfall data are used, and in the second example, monthly median rainfall data are used for calculations. Monthly rainfall data for several locations in Texas are provided in Appendix B. Keep in mind that the basic monthly water balance calculation is Water available (gallons) = Initial volume in storage (gallons) + gallons captured – gallons used. In an especially wet month, gallons in storage + gallons captured may exceed storage capacity; storage capacity could become a limiting factor, or a slightly larger cistern may be considered. Assumptions • Demand of 3,000 gallons/month • Collection efficiency of 85 percent • 0.62 gallons per square foot of roof area per inch of rain • 10,000-gallon storage capacity • 1,000 gallons in storage on January 1 to start out. (The water may have been collected between the time of system completion and new home occupancy, or it may be hauled water; systems designed for irrigation use only should be completed in the fall to collect rainwater during the slow-/non-growth season.) • Irrigation volume is estimated based upon a small ornamental landscape, and limited supplemental irrigation, since this example is used for potable supply. Calculations using Monthly Average Rainfall Data First calculate the number of gallons collected in January. Using the average value of 1.91 inches of rain for January in Dallas (from Appendix B), the number of gallons of rainwater that can be expected to be stored in January from a 2,500-square-foot roof assuming 85% collection efficiency is determined from the equation: Rainfall (inches) x roof area x 0.62 gal/sq ft /in. rain x collection efficiency In this example: 1.97in. rainfall x 2,500sq. ft. catchment x 0.62 gallons/in. rain/sq. ft. x 0.85 collection efficiency = 2,595 gallons To calculate gallons in storage at the end of each month, add the volume of water already in storage (1,000 gallons in this example) to the gallons collected and subtract the monthly demand. 1,000 + 2,595 – 3,000 = 595 gallons available in storage at the end of January This calculation is repeated for each month. To help you follow Table 4-2, please read below: The value in Column E is added to Column F from preceding row and then A is subtracted. If calculated storage amount is zero or less, use zero for the next month. Rainfall exceeding storage capacity is ignored (water lost). The table shows that a collection surface of 2,500 square feet is adequate to meet expected demand (Column F should be more than zero at all times, if not the collection area needs to be increased or the monthly demand should be reduced). Calculations using Monthly Median Rainfall Data Table 4-3 shows the results of using monthly median rainfall (Column D), and performing the same calculations as before. Using monthly median rainfall data is a more conservative method, and is likely to provide a higher reliability than using average rainfall data for system sizing. Homeowners can easily try different values for collection surface and storage capacity using an electronic spreadsheet, downloadable in Excel format from the Texas Water Development Board www.twdb.state.tx.us/assistance/conservation/alternative_technologies/rainwater_harvesting/rain. asp 38
Table 4-2. Sample Water Balance Calculations for Dallas, Texas (Using Average Rainfall and a 2,500-square-foot collection surface) A. B. C. D. E. F. Water Irrigation Total Average Rainfall End-of- demand demand demand rainfall collected month (watering by (gallons) (inches) (gallons) storage hose or (1,000 gal. Month bucket) to start) January 3,000 0 3,000 1.97 2,596 595 February 3,000 0 3,000 2.40 3,162 757 March 3,000 150 3,150 2.91 3,834 1,441 April 3,000 150 3,150 3.81 5,020 3,311 May 3,000 150 3,150 5.01 6,601 6,762 June 3,000 150 3,150 3.12 4,111 7,723 July 3,000 150 3,150 2.04 2,688 7,261 August 3,000 150 3,150 2.07 2,727 6,838 September 3,000 150 3,150 2.67 3,518 7,206 October 3,000 150 3,150 3.76 4,954 9,010 November 3,000 0 3,000 2.70 3,557 9,567 December 3,000 0 3,000 2.64 3,478 10,000* * Note that there were 44 gallons of overflow in December in this example. A 10,000-gallon cistern appears to be appropriate under the given assumptions. Table 4-3. Sample Water Balance Calculations for Dallas, Texas (Using Median Rainfall and a 2,500-square-foot collection surface) A. B. C. D. E. F. Water Irrigation Total Median Rainfall End-of- demand demand demand rainfall collected month (watering by (gallons) storage hose or (1,000 gal. Month bucket) to start) January 3,000 0 3,000 1.80 2,372 372 February 3,000 0 3,000 2.11 2,780 151 March 3,000 150 3,150 2.36 3,109 111 April 3,000 150 3,150 2.98 3,926 887 May 3,000 150 3,150 4.27 5,626 3,363 June 3,000 150 3,150 2.85 3,755 3,968 July 3,000 150 3,150 1.60 2,108 2,926 August 3,000 150 3,150 1.74 2,292 2,068 September 3,000 150 3,150 2.50 3,294 2,212 October 3,000 150 3,150 2.94 3,873 2,935 November 3,000 0 3,000 2.00 2,635 2,570 December 3,000 0 3,000 2.10 2,767 2,337 This table shows that it is critical to start with an initial storage (1,000 gallons), otherwise the cistern may run out of water in February/March, under the given assumptions. 39
Chapter 5 Rainwater Harvesting Guidelines No national standards exist for rainwater Association (ARCSA) is in the process harvesting systems. As a result, efforts of publishing guidelines for potable and abound to give assistance to those nonpotable rainwater harvesting considering using rainwater as a water systems. The guidelines will be available supply at state and local levels. In Texas on the ARCSA website at www.arcsa- the voluntary approach has been the usa.org. hallmark of water conservation efforts, and a Water Conservation Best Other Voluntary Guidelines Management Practices (BMP) Guide A number of University-level programs produced by the Texas Water have published guidelines that are Development Board (TWDB) in 2004 helpful to rainwater designers and included a section on Rainwater planners. Included among them are Harvesting and Condensate Reuse for Texas Cooperative Extension’s use by water providers. (See guidelines and the University of References.) Guidance in other parts of Arizona’s “Harvesting Rainwater for the country ranges from voluntary Landscape Use,” both of which focus on guidelines such as BMPs to codes and capturing rainwater for outdoor ordinances stipulating minimum irrigation. The University of Hawaii standards for various aspects of College of Tropical Agriculture and rainwater harvesting. The wide variety in Human Resources in Hawaii produced approaches is summarized in this chapter “Guidelines on Rainwater Catchment by sharing a few key examples of the Systems in Hawaii,” which has initiatives that are available to assist the information for people using rainwater planner of a rainwater harvesting system. for potable consumption. (See References.) RWH Best Management Practices These guidelines for potable systems Water Conservation Implementation recommend that storage tanks be Task Force Guidelines. In 2003 a constructed of non-toxic material such as statewide Water Conservation steel, fiberglass, redwood, or concrete. Implementation Task Force was Liners used in storage tanks should be appointed by the TWDB under a smooth and of food-grade material legislative mandate to develop approved by the U.S. Food and Drug recommendations for water conservation Administration (Macomber, 2001). for the state of Texas. Best management practices reached by a consensus of the Building Codes Task Force address rainwater harvesting In addition to voluntary effort, some and air conditioner condensate in the states and municipalities are choosing to Task Force Water Conservation Best establish rules. Ohio, Kentucky, Hawaii, Management Practices Guide (TWDB, Arizona, New Mexico, Washington, 2004). West Virginia, Texas, and the U.S. American Rainwater Catchment Virgin Islands are considering or have Systems Association. The American developed rules related to rainwater Rainwater Catchment Systems harvesting. 41
Rules, ordinances, building codes, and building expansion must have a homeowner association covenants provision for a self-sustaining water nationwide run the gamut from requiring supply system, either a well or a rainwater harvesting systems on new rainwater collection area and cistern. construction to prohibiting tanks as an The rules for private water systems in eyesore. the U.S. Virgin Islands state that new In Texas, HB 645, passed by the 78th cisterns must have a minimum capacity Legislature in 2003, prevents of 2,500 gallons per dwelling (Virgin homeowners associations from Islands Code, Title 29, Public Planning implementing new covenants banning and Development). outdoor water-conserving measures such The U.S. Virgin Islands specifies that as composting, water-efficient cisterns for hotels or multi-family landscapes, drip irrigation, and rainwater dwellings have a minimum capacity of harvesting installations. The legislation 10 gallons per square foot of roof area allows homeowners associations to for buildings of one story, and 15 gallons require screening or shielding to obscure per square foot of roof area for multi- view of the tanks. story buildings, although the The State of Ohio has the most extensive requirement is waived for buildings with rules on rainwater harvesting in the access to centralized potable water United States, with code on cistern size systems. and material, manhole openings, outlet The City of Portland, Oregon, requires a drains, overflow pipes, fittings, minimum cistern capacity of 1,500 couplings, and even roof washers. gallons capable of being filled with Ohio’s rules also address disinfection of harvested rainwater or municipal water, private water systems. (See References.) with a reduced pressure backflow prevention device and an air gap Cistern Design, Construction, and protecting the municipal supply from Capacity cross-connection (City of Portland, Cistern design is covered by rules in 2000). some states, often embedded in the rules for hauled water storage tanks. In Ohio, Backflow Prevention and Dual- cisterns and stored water storage tanks Use Systems must have a smooth interior surface, and The option of “dual-supply” systems concrete tanks must be constructed in within a residence – potable harvested accordance with ASTM C913, Standard rainwater supplemented with water from Specification for Precast Concrete a public water system with appropriate Water and Wastewater Structures. backflow prevention – is an option that Plastic and fiberglass tank materials and might be explored for residences which all joints, connections, and sealant must cannot collect enough rainwater. meet NSF/ANSI Standard 61, Drinking Water System Components. In most Texas locations, rainfall occurs seasonally, requiring a large storage In the U.S. Virgin Islands, Bermuda, and capacity to hold enough water collected other Caribbean islands (islands without during rain events to last through the dry large reservoirs or adequate groundwater spells. reserves), all new construction and even 42
Allowing for a connection to the public For instance, Santa Fe County, New water supply system could serve to Mexico, passed the precedent-setting promote harvested rainwater as a regulation requiring rainwater harvesting supplemental water source to customers systems on new residential or already connected to the public water commercial structures of 2,500 square supply infrastructure. feet and larger. A bill requiring rainwater harvesting systems on all new This “conjunctive” use would require an construction narrowly missed passage in appropriate backflow prevention device the New Mexico legislature (Darilek, to keep rainwater from entering the 2004; Vitale, 2004) public water supply due to a drop in pressure in the utility’s distribution The City of Tucson, Arizona, has system. instituted requirements for water harvesting in its land use code as a The City of Portland has approved means of providing supplemental water supplemental use of public utility water for on-site irrigation. In fact, “storm at a residence since 1996. The code water and runoff harvesting to includes specific guidance for design supplement drip irrigation are required and installation of the system. It also elements of the irrigation system for limits rainwater to nonpotable uses. The both new plantings and preserved Portland Office of Planning and vegetation” (City of Tucson Code, Development publishes a RWH Code Chapter 23). Guide which includes FAQ and the relevant code sections (City of Portland, Water harvesting in Tucson is also 2000). intended to help in meeting code requirements for floodplain and erosion The State of Washington Building Codes hazard management (City of Tucson Council in 2002 developed guidelines for installation of rainwater harvesting Code, Chapter 26). systems at commercial facilities. They 2005 Rainwater Harvesting are similar to the City of Portland Legislation guidelines mentioned above, but require a larger cistern size, determined by the The Texas Legislature passed House Bill size of the catchment area, which is (HB) 2430 in May 2005, establishing a limited to roof areas. In 2003, the rainwater harvesting evaluation Washington State Legislature approved a committee to recommend minimum 10 percent reduction in stormwater fees water quality guidelines and standards for any commercial facility that installed for potable and nonpotable indoor uses a rainwater harvesting system in of rainwater. The committee will also compliance with the guidelines recommend treatment methods for (Washington State Legislature, 2003). indoor uses of rainwater, methods by which rainwater harvesting systems Required Rainwater Harvesting could be used in conjunction with Systems existing municipal water systems, and Perhaps the most supportive ordinances ways in which that the state can further are those requiring rainwater harvesting promote rainwater harvesting. The in new construction. committee consists of representatives from the Texas Water Development Board, Texas Commission on 43
Environmental Quality, Department of NSF International, NSF/ANSI Standard State Health Services, and the Texas 61, Drinking Water System Section of the American Water Works Components, Association. The committee will provide www.nsf.org/business/water_distribut its recommendations to the Legislature ion/standards.asp?program=WaterDis by December 2006. tributionSys Ohio Department of Health Final Rules, References 3701-28-09 Continuous Disinfection, www.odh.ohio.gov/Rules/Final/Chap ASTM. 2004. ASTM C913-98 standard 28/Fr28_lst.htm specification for precast concrete water and wastewater structures. In: Texas Cooperative Extension. 2004. ASTM Book of standards. Rainwater Harvesting. Bryan (TX): Texas Cooperative Extension. City of Portland. 2000. Code guide. Portland (OR): Office of Planning Texas Water Development Board, Water and Development. 18 p. Conservation Best Management Practices Guide, p 96-101, City of Tucson Code, Chapter 23, Land www.twdb.state.tx.us/assistance/cons Use Code, Section 3.7.4.5B. 2004. ervation/TaskForceDocs/WCITFBM City of Tucson Code, Chapter 26, PGuide.pdf Floodplain and Erosion Hazard Vitale L. 2004 Mar 11. [Personal Management, Section 26-10, communication]. Sante Fe County. Detention/retention systems. 2004. Virgin Islands Code, Title 29, Public City of Tucson, Water Harvesting Planning and Development; Chapter Guidance Manual, 5, Building Code; Section 308, Water dot.ci.tucson.az.us/stormwater/educat supply, cisterns, gutters, downspouts, ion/waterharvest.htm wells. 2004. Darilek A. 2004 Mar 11. [Personal Washington State Legislature. 2003 Mar communication]. Office of the New 13. House Bill 2088. Mexico State Engineer. Waterfall P. 1998. Harvesting rainwater Macomber P. 2001. Guidelines on for landscape use. Tucson (AZ): The rainwater catchment systems for University of Arizona College of Hawaii. Manoa (HI): College of Agriculture and Life Sciences. 39 p. Tropical Agriculture and Human Resources, University of Hawaii at Welsh DF, Welch WC, Duble RL. 2001. Manoa. 51 p. Xeriscape…Landscape Water Conservation. Bryan (TX): Texas Cooperative Extension. 16 p. 44
Chapter 6 Cost Estimation Developing a budget for a rainwater both potable use and for irrigation. It harvesting system may be as simple as also has a brief section on comparing adding up the prices for each of the costs with other types of water supply. components and deciding what one can The single largest expense is the storage afford. For households without access to tank, and the cost of the tank is based reliable groundwater or surface water, upon the size and the material. Table 6-1 and too remotely located to hook up to shows a range of potential tank materials the existing potable supply and costs per gallon of storage. The size infrastructure, the information in this of storage needed (see Chapter 4, Water chapter will assist in determining how Balance and System Sizing) and the large a system can be installed for a set intended end use of the water will dictate budget, and the range of costs for an which of the materials are most ideal system. For some, the opportunity appropriate. Costs range from a low of to provide for all or a portion of their about $0.50 per gallon for large water needs with rainwater is an exercise fiberglass tanks to up to $4.00 per gallon in comparing the costs with other for welded steel tanks. options to determine which is most cost- effective. This chapter provides some As tank sizes increase, unit costs per information on cost ranges for standard gallon of storage decreases. components of rainwater systems for 45
Table 6-1. Storage Tank Cost Size Comments Fiberglass $0.50–2.00/gallon 500–20,000 gallons Can last for decades w/out deterioration; easily repaired; can be painted Concrete $0.30–1.25/gallon Usually 10,000 gallons Risks of cracks and leaks or more but these are easily repaired; immobile; smell and taste of water sometimes affected but the tank can be retrofitted with a plastic liner Metal $0.50–1.50/gallon 150–2,500 gallons Lightweight and easily transported; rusting and leaching of zinc can pose a problem but this can be mitigated with a potable- approved liner Polypropylene $0.35–1.00/gallon 300–10,000 gallons Durable and lightweight; black tanks result in warmer water if tank is exposed to sunlight; clear/translucent tanks foster algae growth Wood $2.00/gallon 700–50,000 gallons Esthetically pleasing, sometimes preferable in public areas and residential neighborhoods Polyethylene $0.74–1.67/gallon 300–5,000 gallons Welded Steel $0.80–$4.00/gallon 30,000–1 million gallons Rain Barrel $100 55–100 gallons Avoid barrels that contain toxic materials; add screens for mosquitoes Gutters and downspouts (Table 6-2) are approximately the same cost. For those needed to collect the water and route it desiring professionally installed to the tank. Two types of gutters are materials, costs range from $3.50 to $12 available for the “do-it-yourselfers”: per foot of gutter, including materials vinyl and plastic, which are available for and installation, in 2004. 46
Table 6-2. Gutters Cost Comments Vinyl $.30/foot Easy to install and attach to PVC trunk lines Plastic $.30/foot Leaking, warping and breaking are common problems Aluminum $3.50-6.25/foot Must be professionally installed Galvalume $9-12/foot Mixture of aluminum and galvanized steel; must be professionally installed Some method of discarding the first The roof washer, placed just ahead of the flush of rain from the roof is necessary storage tank, usually consists of a tank to remove debris. The simplest method with leaf strainers and a filter. A is a vertical PVC standpipe, which fills commercially available model has a with the first flush of water from the series of baffles and a 30-micron filter. roof, then routes the balance of water to the tank. 47
Table 6-3. Roof Washers Cost Maintenance Comments Box Washer $400-800 Clean the filter after Neglecting to clean every substantial rain the filter will result in restricted or blocked water flow and may become a source or contamination Post Filtering w/ Sand $150-500 Occasionally Susceptible to Filter backwash the filter freezing; a larger filter is best Smart-Valve $50 for kit Occasional cleaning Device installed in a Rainwater Diverter diversion pipe to Kit make it self-flushing and prevent debris contamination; resets automatically Roof washers consist of a tank, usually Table 6-4 shows the ranges for pump between 30- and 50-gallon capacity, costs including pressure tanks. Demand- with leaf strainers and a filter. A roof activated pumps such as Grundfos may washer is a critical component of potable not require a pressure tank, and can often systems and is also needed to filter small provide enough water to meet a home’s particles to avoid clogging drip irrigation demand for instantaneous flow. Careful emitters. A wide range of equipment is thought should be given to the available with different flow capacity possibility of multiple simultaneous and maintenance requirements. In Table demands upon the system in determining 6-3 a list of different equipment used to the appropriate size pump. The range for intercept and pre-filter the water shows a pump costs runs from $385 for the low- range of costs from $50 to more than end tankless pump, to more than $1,000 $800. It is important that the rainwater for the combined price of a high-end harvester pick a roof washer that is pump and pressure tank. adequate for the size of collection area. 48
Table 6-4. Pumps and Pressure Tanks Cost Comments Grundfos MQ Water Supply $385-600 Does not require a separate System pressure tank Shallow Well Jet Pump or $300-600 These require a separate Multi-Stage Centrifugal Pump pressure tank Pressure Tank $200-500 Galvanized tanks are cheaper than bladder tanks but often become waterlogged, and this will wear out the pump more rapidly For those planning a potable system, or widely depending upon intended end- if a drip irrigation system is used, some use, the desired water quality, and sort of filtration is necessary. Rainwater preferences of the user. As shown in harvesting suppliers can assist the end Table 6-5, combined filtration/ user in purchasing the right equipment disinfection costs can cost up to $1,000 for his/her needs and the expected or more. Chapter 2, Rainwater demand. Harvesting System Components, will assist you in choosing the right filtration It is important for the end user intending and/or disinfection equipment for your to use rainwater for potable supply to include disinfection among the water system. treatment components. The costs vary 49
Table 6-5. Filtering/Disinfection Cost Maintenance Effectiveness Comments Cartridge Filter $20-60 Filter must be Removes A disinfection changed particles >3 treatment is also regularly microns recommended Reverse Osmosis $400-1500 Change filter Removes A disinfection Filter when clogged particles >0.001 treatment is also (depends on the microns recommended turbidity) UV Light $350-1000; $80 Change UV bulb Disinfects Water must be Disinfection to replace UV every 10,000 filtered water filtered prior to bulb hours or 14 provided there exposure for months; the are <1,000 maximum protective cover coliforms per effectiveness must be cleaned 100 milliliter regularly Ozone $700-2600 Effectiveness Less effective in Requires a pump Disinfection must be high turbidity, to circulate the monitored with can be improved ozone molecules frequent testing with pre-filtering or an in-line monitor ($1,200 or more) Chlorine $1/month manual Monthly dose High turbidity Excessive Disinfection dose or a $600- applied manually requires a higher chlorination may $3000 automatic concentration or be linked to self-dosing prolonged negative health system exposure but this impacts. can be mitigated by pre-filtering recommendations for regular Operating Costs maintenance. But proper operation and There are also operating costs that maintenance of the system does add to should be considered as you prepare total costs. your budget. As with any water treatment system, the cleaner the water Filter cartridges should be replaced per needs to be, the greater the effort manufacturer’s specifications, based required to maintain the system. upon the rate of water use. Fortunately, with filter cartridges, this Some of the operating costs and time just means regular replacement of the expenditures necessary for system cartridges, and with the disinfection maintenance are regularly cleaning system, following the manufacturers’ gutters and roof washers, checking the 50
system for leaks by monitoring water with no guarantee of hitting a reliable levels, and paying close attention to source of water. The deeper the well, the water use rates to determine if an more expensive the effort will be. Also, invisible leak has sprung. Although the well water can have very high TDS “do-it-yourselfers” can handle all of levels in some aquifers, resulting in these tasks with little added financial “hard” water. Rainwater is naturally soft burden, the time for regular maintenance and has become a preferred option in and operation must be set aside to some parts of rural central Texas with operate a successful system. costs lower than or equal to those of drilling a well, and reliability high Comparing to Other Sources of enough to justify reliance on weather Water patterns, rather than on an aquifer’s In some areas of Texas the cost of water quality and quantity. drilling a well can be as high as $20,000 51
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Chapter 7 Financial and Other Incentives Financial incentives and tax exemptions regulations did not raise a facility’s encourage the installation of rainwater property taxes, by adding Section 11.31 harvesting systems. The Texas to Chapter 11, and Section 26.045 to Legislature has passed bills, and some Chapter 26 of the Texas Tax Code. local taxing entities have adopted rules The Texas Commission on that provide tax exemptions for Environmental Quality (TCEQ) rainwater harvesting systems. A few established procedures and mechanisms public utilities have implemented rebate for use determination under Texas programs and rain barrel distribution Administrative Code (TAC) Title 30, events that encourage rainwater Chapter 17. harvesting by residential, commercial, and industrial customers. In addition to To qualify for the property tax financial incentives, performance exemption, (1) a facility must first contracting provisions in state code can receive a determination from the TCEQ be used to encourage installation of that the property is used for pollution rainwater harvesting systems. This control purposes, and (2) the applicant chapter includes a brief description of then submits this use determination to methods for determining the appropriate the local tax appraisal district to obtain size of an incentive by local the property tax exemption. governments. The Application and Instructions for Use In addition to financial incentives, Determination for Pollution Control administrative contracting rules for state Property and Predetermined Equipment and local governments encourage the use List, as well as instructions for applying of rainwater harvesting as an alternative for Property Tax Exemptions for water source in Texas. Pollution Control Property, are downloadable from the TCEQ website. Tax Exemptions (See References.) Property tax exemption for commercial Property tax exemptions extended (State- installations (State-wide exemption) wide) A constitutional amendment passed as Passed in 2001 by the 77th Texas Proposition 2 by Texas voters in Legislature, Senate Bill 2 amended November 1993 exempted pollution Section 11.32 of the Texas Tax Code to control equipment, including water- allow taxing units of government the conserving equipment at nonresidential option to exempt from taxation all or buildings, from property taxes. part of the assessed value of the property Rainwater harvesting equipment at on which water conservation commercial installations is considered modifications have been made. The water-conserving equipment. The intent taxing entity designates by ordinance or of this amendment to Article VIII of the law the list of eligible water Texas Constitution was to ensure that conservation initiatives, which may capital expenditures undertaken to include rainwater harvesting systems. comply with environmental rules and 53
rainwater harvesting equipment or County property tax exemptions supplies, water recycling and reuse Homeowners planning to install equipment or supplies, or other rainwater harvesting systems should equipment.” check with their respective county appraisal districts for guidance on An application for sales tax exemption is exemption from county property taxes. included as Appendix D, or can be Links to some county appraisal districts, downloaded from the Office of the State as well as the Office of the State Comptroller. (See References.) Comptroller’s Application for Water Conservation Initiatives Property Tax Municipal Incentives Exemption, can be found online. (See In addition to tax exemptions, two Texas References.) cities offer financial incentives in the form of rebates and discounts to their Hays County is one of the fastest- customers who install rainwater growing counties in Texas, and is also harvesting and condensate recovery the county with the most rapidly systems. increasing number of new rainwater harvesting installations in the state. Hays City of Austin Rainwater Harvesting County encourages rainwater harvesting Programs with a $100 rebate on the development The City of Austin Water Conservation application fee. Department promotes both residential and commercial/industrial rainwater For rainwater harvesting systems serving harvesting. (See References.) The City as the sole source of water for a of Austin sells 75-gallon polyethylene residence, Hays County grants a rain barrels to its customers below cost, property tax exemption from county at $60 each, up to four rain barrels per taxes for the value of the rainwater customer. City of Austin customers who harvesting system. Guidelines for purchase their own rain barrels are rainwater harvesting benefits and eligible for a $30 rebate. qualification can be found at the Hays County website. (See References.) Customers may also receive a rebate of up to $500 on the cost of installing a pre- Homeowners in other parts of the state approved rainwater harvesting system. should consider approaching their local The rebate application includes a government to see if such a property tax formula to calculate optimum tank size exemption could be passed in their and a list of area suppliers and locale. installation contractors. (See Sales Tax Exemption (State-wide) References.) Senate Bill 2 exempts rainwater Commercial entities may be eligible for harvesting equipment and supplies from as much as a $40,000 rebate against the sales tax. Senate Bill 2 amended cost of installing new equipment and Subchapter H of the Tax Code by adding processes to save water under the Section 151.355, which states: Commercial Incentive Program. (See “Water-related exemptions. The References.) following are exempted from taxes New commercial or industrial sites that imposed by this chapter: (1) develop capacity to store sufficient water 54
on-site for landscape irrigation may be Best Management Practices Guide (p. able to receive an exemption from 118 to 130), gives an example and the installing an irrigation meter. steps in calculating the net present value of conserved water. San Antonio Water System Large-Scale Retrofit This approach requires the utility to Rainwater harvesting projects are estimate the potential for water savings eligible for up to a 50-percent rebate due to rainwater harvesting systems under San Antonio Water System’s installed and the likely number of (SAWS) Large-Scale Retrofit Rebate participants in a program. Program. (See References.) SAWS will rebate up to 50 percent of the installed Rainwater Harvesting at State cost of new water-saving equipment, Facilities including rainwater harvesting systems, In 2003, the 78th Texas Legislature, to its commercial, industrial, and second session, passed HB9, which institutional customers. Rebates are encourages rainwater harvesting and calculated by multiplying acre-feet of water recycling at state facilities. The water conserved by a set value of bill requires that the Texas Building and $200/acre-foot. Equipment and projects Procurement Commission appoint a task must remain in service for 10 years. The force charged with developing design water savings project is sub-metered, recommendations to encourage and water use data before and after the rainwater harvesting and water recycling retrofit are submitted to SAWS to at state facilities built with appropriated determine if conservation goals are met. money. To qualify for the rebate, an engineering The intent of HB9 is to promote the proposal and the results of a professional conservation of energy and water at state water audit showing expected savings buildings. The bill requires that before a are submitted. state agency may use appropriated The rebate shortens the return on money to make a capital expenditure for investment period, giving an incentive to a state building, the state agency must industry to undertake water-conserving determine whether the expenditure could projects. be financed with money generated by a utility cost-savings contract. Determining How Much of a Financial Incentive a Utility May Wish to Offer If it is determined to be not practicable To determine whether a municipal utility to finance construction with utility cost should consider offering a rebate or savings, rainwater harvesting and water financial incentive to stimulate the use of recycling are encouraged by HB9. rainwater harvesting, benefits and costs In addition the Texas Education Code must be presented on an economic basis. (Section 61.0591) provides an incentive This is most easily accomplished by to institutes of higher education for condensing the factors into terms of achieving goals set by the Texas Higher dollars per acre-foot ($/AF) and Education Coordinating Board (THECB) comparing that to the cost of building a including: new water supply project. The spreadsheet included in the TWDB’s Report No. 362, Water Conservation 55
“energy conservation and water amendments that increase the water- conservation, rainwater harvesting, holding capacity of the soil, and water reuse.” including compost.” The code states that not less than 10 “rainwater harvesting equipment and percent of THECB total base funding equipment to make use of water will be devoted to incentive funding. collected as part of a stormwater system installed for water quality Performance Contracting control.” Another means of encouraging the “equipment needed to capture water installation of water- or energy-efficient from nonconventional, alternate equipment is to pay for the equipment sources, including air-conditioning through the savings in utility bills. This condensate or graywater, for method of financing water conservation nonpotable uses, and metering has been used by commercial and equipment needed to segregate water industrial consumers, and is written into use in order to identify water state code for government buildings in conservation opportunities or verify several locations. water savings.” The Texas Education Code (Chapter Performance contracts serve as a win- 44.901 and Chapter 51.927), the Texas win opportunity for school districts and Local Government Code (Chapter institutes of higher education to effect 302.004), and the State Government improvements on facilities for water- Code (Chapter 2166.406) allow public and energy-conservation without schools, institutes of higher education, incurring net construction costs. state building facilities, and local governments to enter into performance The State Energy Conservation Office, contracts. Performance contracting in Suggested Water Efficiency allows a facility to finance water- and Guidelines for Buildings and Equipment energy-saving retrofits with money at Texas State Facilities, recommends saved by the reduced utility expenditures that use of alterative water sources be made possible by the retrofit. In other explored for landscape irrigation use. words, the water- and energy-conserving (See References.) Suggested water measures pay for themselves within the sources include captured stormwater or contracted period. More information on rainwater, air-conditioner condensate, performance contracting can be found on water from basement sump pump the State Energy Conservation Office discharge, and other sources, in website. (See References.) accordance with local plumbing codes. Following are descriptions of alternative water sources that are eligible for References performance contracts: City of Austin Water Conservation “landscaping measures that reduce Department, watering demands and capture and www.ci.austin.tx.us/watercon/ hold applied water and rainfall, including: (a) landscape contouring, City of Austin Water Conservation including the use of berms, swales, Department, commercial process and terraces; and (b) the use of soil evaluations and rebates, 56
www.ci.austin.tx.us/watercon/comme www.tnrcc.state.tx.us/exec/chiefeng/p rcial.htm rop2/0611.doc City of Austin Water Conservation Texas county appraisal districts, Department, rainbarrel rebate, www.texascad.com www.ci.austin.tx.us/watercon/rainwat Texas Statutes Tax Code, er.htm www.capitol.state.tx.us/statutes/tx.toc Hays County, rainwater harvesting .htm benefits and qualification, Texas Water Development Board, Water www.co.hays.tx.us/departments/envir Conservation Best Management ohealth/forms.php Practices Guide, p 96-101, Office of the State Comptroller, www.twdb.state.tx.us/assistance/cons application for sales tax exemption, ervation/TaskForceDocs/WCITFBM www.window.state.tx.us/taxinfo/taxf PGuide.pdf orms/01-3392.pdf Office of the State Comptroller, application for water conservation initiatives property tax exemption, www.window.state.tx.us/taxinfo/taxf orms/50-270.pdf San Antonio Water System, large-scale retrofit rebate program, www.saws.org/conservation/commer cial/retrofit.shtml State Energy Conservation Office, www.seco.cpa.state.tx.us/sa_perform contract.htm State Energy Conservation Office, Suggested Water Efficiency Guidelines for Buildings and Equipment at Texas State Facilities, www.seco.cpa.state.tx.us/waterconser vation.pdf Texas Commission on Environmental Quality, application and instructions for use determination for pollution control property and predetermined equipment list, www.tnrcc.state.tx.us/exec/chiefeng/p rop2/guidance.pdf Texas Commission on Environmental Quality, property tax exemptions for pollution control property, 57
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Appendix A References ASTM. 2004. ASTM C913-98 standard City of Tucson Code. 2004. Chapter 26, specification for precast concrete Floodplain and Erosion Hazard Area water and wastewater structures. In: Regulations, Section 26-10, ASTM Book of standards. Detention/retention systems. American Rainwater Catchment Systems College of Tropical Agriculture and Association. 2003. First American Human Resources. 2000. Rainwater rainwater harvesting conference catchment systems. Manoa (HI): proceedings. Austin (TX). 2003 Aug University of Hawaii at Manoa. 4 p. 21-22. County of Hawaii. Undated. Guidelines American Water Works Association. for owners of rain catchment water 1999. Residential end uses of water. systems. Hilo (HI): County of Denver (CO): American Water Hawaii. 5 p. Works Association Research Darilek A. 2004 Mar 11. [Personal Foundation. 310 p. communication]. Office of the New Banks S, Heinichen R. 2004. Rainwater Mexico State Engineer. collection for the mechanically Darrow K, Saxenian M. 1986. challenged. Dripping Springs (TX): Appropriate technology sourcebook: Tank Town Publishing. 108 p. a guide to practical books for village Campbell S. 1983. Home water supply: and small community technology. how to find, filter, store, and conserve Stanford (CA): Volunteers in Asia. it. Charlotte (VT): Garden Way 800 p. Publishing. 240 p. Frasier G. 1974. Water harvesting City of Albuquerque. 1999. Rainwater symposium proceedings. Phoenix harvesting: supply from the sky. (AZ). 1974 Mar 26-28. Albuquerque (NM): Water Use and Gould J, Nissen-Petersen E. 1999. Conservation Bureau. 32 p. Rainwater catchment systems for City of Albuquerque. 2000. A waterwise domestic rain: design construction guide to rainwater harvesting. and implementation. London: Albuquerque (NM): Water Use and Intermediate Technology Conservation Bureau. 4 p. Publications. 335 p. City of Austin. 1995. Sustainable Kinkade-Levario H. 2004. Forgotten building sourcebook. Austin (TX): rain. City of Austin Environmental and Krishna H. 2001. Rainwater catchment Conservation Services Department. systems in Texas. Proceedings of the 400 p. 10th International Conference on City of Portland. 2000. Code guide. Rainwater Catchment Systems of the Portland (OR): Office of Planning International Rainwater Catchments and Development. 18 p. Systems Association; 2001 Sep 10- 14; Mannheim, Germany. A1
Krishna H. 2003. An overview of Radlet J, Radlet P. 2004. Rainwater rainwater harvesting systems and harvesting design and installation guidelines in the United States. workshop. Boerne (TX): Save the Proceedings of the First American Rain. Rainwater Harvesting Conference; Speidel DH, Ruesdisili LC, Agnew AF. 2003 Aug 21-23; Austin (TX). 1987. Perspectives on water uses and Lye D. 1992. Microbiology of rainwater abuses. New York (NY): Oxford cistern systems: a review. Journal of University Press. 400 p. Environmental Science and Health Spence CC. 1980. The rainmakers: A27(8):2123-2166. American pluviculture to World War Lye D. 2002. Health risks associated II. Lincoln (NE): University of with consumption of untreated water Nebraska Press. 181 p. from household roof catchment Steadman P. 1975. Energy, environment systems. Journal of the American and building. New York (NY): Water Resources Association Cambridge University Press. 287 p. 38(5):1301-1306. Steward JC. 1990. Drinking water Macomber P. 2001. Guidelines on hazards: how to know if there are rainwater catchment systems for toxic chemicals in your water and Hawaii. Manoa (HI): College of what to do if there are. Hiram (OH): Tropical Agriculture and Human EnviroGraphics. Resources, University of Hawaii at Manoa. 51 p. Still GT, Thomas TH. 2003. Sizing and optimally locating guttering for Morgan D, Travathan S. 2002. Storm rainwater harvesting. Proceedings of water as a resource: how to harvest the 11th International Conference on and protect a dryland treasure. Santa Rainwater Catchment Systems; 2003 Fe (NM): City of Santa Fe. 24 p. Aug 25-29; Mexico City (MX). National Academy of Sciences. 1974. Thomas PR, Grenne GR. 1993. More water for arid lands. Rainwater quality from different roof Washington (DC): National Academy catchments. Water Science of Sciences. 149 p. Technology (28):290-99. National Park Service. 1993. Guiding Texas Cooperative Extension. 2004. principles of sustainable Rainwater Harvesting. Bryan (TX): development. Denver (CO): Texas Cooperative Extension. Government Printing Office. Texas Water Development Board. 1997. Pacey A, Cullis A. 1986. Rainwater Texas guide to rainwater harvesting. harvesting: the collection of rainwater Austin (TX): Texas Water and runoff in rural areas. London Development Board. 58 p. (UK): Intermediate Technology Productions. 216 p. Texas Water Development Board. 2002. Water for Texas – 2002. Austin (TX): Phillips A. 2003. City of Tucson water Texas Water Development Board. harvesting guidance manual. Tucson 155 p. (AZ): City of Tucson. 36 p. A2
Vasudevan L. 2002. A study of www.ci.austin.tx.us/watercon/rainwat biological contaminants in rainwater er.htm collected from rooftops in Bryan and City of Austin Green Builder Program, College Station, Texas [masters www.ci.austin.tx.us/greenbuilder/ thesis]. College Station (TX): Texas A&M University. 180 p. City of Tucson. 2003. Water Harvesting Guidance Manual, Virgin Islands Code. 2004. Title 29, dot.ci.tucson.az.us/stormwater/educat Public Planning and Development; ion/waterharvest.htm Chapter 5, Building Code; Section 308, Water supply, cisterns, gutters, City of Tucson Code. 2004. Chapter 23, downspouts, wells. Land Use Code, Section 3.7.4.5B, Use of Water, Vitale L. 2004 Mar 11. [Personal www.tucsonaz.gov/planning/luc/luc.h communication]. Sante Fe County. tm Waterfall P. 1998. Harvesting rainwater Consortium for Energy Efficiency, list of for landscape use. Tucson (AZ): The clothes washers, University of Arizona College of www.cee1.org/resid/seha/rwsh/rwsh- Agriculture and Life Sciences. 39 p. main.php3 Washington State Legislature. 2003 Mar Green Builders, www.greenbuilder.com 13. House Bill 2088. Hays County, guidelines for rainwater Welsh DF, Welch WC, Duble RL. 2001. harvesting benefits and qualifications, Xeriscape…Landscape Water www.co.hays.tx.us/departments/envir Conservation. Bryan (TX): Texas ohealth/forms.php Cooperative Extension. 16 p. International Rainwater Catchment Systems Association, www.ircsa.org Websites National Climate Data Center, American Rainwater Catchment Systems www.ncdc.noaa.gov Association, www.arcsa-usa.org National Oceanographic and Application for Water Conservation Atmospheric Administration, Initiatives Property Tax Exemption, www.noaa.gov www.window.state.tx.us/taxinfo/taxf NSF International, filter performance, orms/50-170.pdf www.nsf.org/certified/DWTU/ City of Austin Water Conservation NSF International, NSF/ANSI Standard Department, 61, Drinking Water System www.ci.austin.tx.us/watercon/ Components, City of Austin Water Conservation www.nsf.org/business/water_distribut Department, commercial process ion/standards.asp?program=WaterDis evaluations and rebates, tributionSys www.ci.austin.tx.us/watercon/comme Office of Arid Land Studies Desert rcial.htm Research Unit, Casa del Agua, City of Austin Water Conservation www.ag.arizona.edu/OALS/oals/dru/ Department, rainbarrel rebate, casadelagua.html A3
Office of the State Comptroller, for use determination for pollution application for sales tax exemption, control property and predetermined www.window.state.tx.us/taxinfo/taxf equipment list, orms/01-3392.pdf www.tnrcc.state.tx.us/exec/chiefeng/p rop2/guidance.pdf Office of the State Comptroller, application for water conservation Texas Commission on Environmental initiatives property tax exemption, Quality, chemical constituents, www.window.state.tx.us/taxinfo/taxf www.tnrcc.state.tx.us/airquality.html orms/50-270.pdf Texas Commission on Environmental Ohio Department of Health Final Rules, Quality, property tax exemptions for 3701-28-09 Continuous Disinfection, pollution control property, www.odh.ohio.gov/Rules/Final/Chap www.tnrcc.state.tx.us/exec/chiefeng/p 28/Fr28_lst.htm rop2/0611.doc Organization of American States, Texas county appraisal districts, Rainwater Harvesting from Rooftop www.texascad.com Catchments, Texas Department of State Health www.oas.org/usde/publications/Unit/ Services, county health departments, oea59e/ch10.htm www.dshs.state.tx.us/regions/default. Rain Water Harvesting and Waste Water shtm Systems Pty Ltd., Texas Department of State Health www.rainharvesting.com.au Services, testing for fecal coliforms, San Antonio Water System, large-scale www.dshs.state.tx.us/lab/default.shtm retrofit rebate program, Texas Evapotranspiration, www.saws.org/conservation/commer texaset.tamu.edu cial/retrofit.shtml Texas Legal Directory, county appraisal State Energy Conservation Office, districts, www.texascad.com www.seco.cpa.state.tx.us/sa_perform contract.htm Texas Legislature Online, www.capitol.state.tx.us/ State Energy Conservation Office, Suggested Water Efficiency Texas Master Gardeners, Guidelines for Buildings and aggiehorticulture.tamu.edu/mastergd/ Equipment at Texas State Facilities, mg.html www.seco.cpa.state.tx.us/waterconser Texas Statutes Education Code, vation.pdf www.capitol.state.tx.us/statutes/ed.to Texas Administrative Code, c.htm www.sos.state.tx.us/tac/ Texas Statutes Local Government Code, Texas Commission on Environmental www.capitol.state.tx.us/statutes/lg.toc Quality, Air Quality Monitoring, .htm www.tceq.state.tx.us/nav/data/pm25. Texas Statutes Tax Code, html www.capitol.state.tx.us/statutes/tx.toc Texas Commission on Environmental .htm Quality, application and instructions A4
Texas Water Development Board, Water www.twdb.state.tx.us/assistance/cons Conservation Best Management ervation/consindex.asp Practices Guide, p 96-101, United States Environmental Protection www.twdb.state.tx.us/assistance/cons Agency, drinking water requirements, ervation/TaskForceDocs/WCITFBM www.epa.gov/safewater/mcl.html PGuide.pdf United States Environmental Protection Texas Water Development Board Agency Safe Drinking Water Act, Conservation, www.epa.gov/safewater/sdwa/sdwa.htm A5
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Appendix B Rainfall Data The following data are provided for representative Texas cities in various geographical areas to assist in assessing the optimal storage size for a particular rainwater harvesting system. Each rainwater harvesting system designer should assess the variables of water demand, rainfall, catchment surface area, storage capacity, and risk tolerance when designing a rainwater harvesting system, especially one intended to be the sole water source. Abilene Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 4.35 3.60 5.16 6.80 13.17 9.60 7.52 8.18 11.03 10.68 4.60 6.28 Median 0.81 0.73 0.90 1.88 2.47 2.30 1.69 1.62 2.25 2.09 0.94 0.77 Average 1.00 1.05 1.17 2.05 3.22 2.90 2.03 2.40 2.71 2.56 1.24 1.03 Average annual rainfall 23.36 Amarillo Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.04 0.01 0.10 0.28 0.03 0.00 0.00 0.00 Maximum 2.33 1.83 4.01 5.84 9.81 10.73 7.59 7.55 5.02 6.34 2.26 4.52 Median 0.33 0.42 0.58 0.86 2.45 3.08 2.59 2.79 1.61 0.97 0.43 0.35 Average 0.52 0.55 0.93 1.18 2.67 3.40 2.80 2.93 1.84 1.44 0.59 0.53 Average annual rainfall 19.39 Austin Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.09 0.00 0.00 0.00 Maximum 9.21 6.56 6.03 9.93 9.98 14.96 10.54 8.90 7.44 12.31 7.95 14.16 Median 1.27 2.30 1.73 2.20 3.68 2.89 1.15 1.27 2.98 2.82 1.88 1.42 Average 1.77 2.37 1.90 2.83 4.33 3.54 1.73 2.18 3.17 3.63 2.25 2.26 Average annual rainfall 31.96 Brady Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.10 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 6.40 5.30 4.30 6.02 8.00 7.70 13.55 11.30 9.45 7.04 10.40 7.90 Median 0.60 1.26 0.90 1.78 3.10 1.87 0.85 1.34 2.40 1.70 1.10 0.70 Average 1.03 1.50 1.26 2.07 3.40 2.40 1.80 2.01 2.86 2.34 1.43 1.28 Average annual rainfall 23.38 A7
Brownsville Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.07 0.34 0.01 0.00 Maximum 4.79 10.25 5.72 10.35 9.12 8.52 9.43 9.56 20.18 17.12 7.69 3.98 Median 0.77 0.84 0.41 0.84 1.86 2.22 0.96 2.45 4.69 2.92 0.90 0.78 Average 1.31 1.38 0.80 1.62 2.39 2.55 1.50 2.69 5.19 3.62 1.55 1.10 Average annual rainfall 25.70 College Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.22 0.1 0.29 0.08 0.23 0.09 0 0 0.32 0 0.19 0.23 Maximum 15.6 9.82 6.07 12.5 11.38 12.63 7.06 10.63 12.13 12.91 8.33 10.72 Median 2.205 2.72 2.12 3.75 4.515 2.895 1.97 1.84 4.12 3.18 2.92 2.635 Average 2.87 2.88 2.5 3.77 4.73 3.79 2.24 2.43 4.3 3.64 3.07 3.15 Average annual rainfall 38.75 Corpus Christi Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.01 0.00 0.00 0.00 0.00 0.03 0.00 0.10 0.49 0.00 0.00 0.01 Maximum 10.78 8.11 4.89 8.04 9.38 13.35 11.92 14.79 20.33 11.88 5.24 9.80 Median 0.99 1.36 0.78 1.39 2.70 2.43 1.04 2.64 4.00 2.60 1.34 0.90 Average 1.54 1.85 1.36 2.03 3.12 3.16 1.80 3.28 5.21 3.50 1.57 1.59 Average annual rainfall 30.00 Dallas Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.25 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.18 0.13 Maximum 8.46 7.60 8.70 15.40 13.74 10.30 7.34 5.12 10.67 14.00 7.54 8.90 Median 1.80 2.11 2.36 2.98 4.27 2.85 1.60 1.74 2.50 2.94 2.00 2.10 Average 1.97 2.40 2.91 3.81 5.01 3.12 2.04 2.07 2.67 3.76 2.70 2.64 Average annual rainfall 35.10 El Paso Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 Maximum 2.23 1.69 2.26 1.42 4.22 3.18 5.53 5.57 6.68 3.12 1.63 3.29 Median 0.29 0.34 0.18 0.09 0.10 0.36 1.18 1.06 0.96 0.55 0.24 0.42 Average 0.42 0.40 0.30 0.21 0.32 0.70 1.57 1.45 1.38 0.71 0.36 0.61 Average annual rainfall 8.43 A8
Houston Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.36 0.38 0.11 0.43 0.04 0.26 0.45 0.31 0.80 0.05 0.41 0.64 Maximum 9.78 5.99 8.52 10.92 14.39 16.28 8.10 9.42 11.35 16.05 10.07 9.34 Median 2.82 2.63 3.19 2.59 5.02 3.55 2.69 3.52 3.92 3.79 3.27 3.41 Average 3.68 2.95 3.40 3.54 5.36 5.07 3.05 3.69 4.31 4.63 4.09 3.54 Average annual rainfall 48.45 Lubbock Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 4.05 2.51 3.34 5.63 13.38 8.43 7.20 8.85 8.55 10.80 2.67 2.24 Median 0.33 0.39 0.63 1.08 2.23 2.37 2.07 1.78 1.87 0.98 0.45 0.42 Average 0.52 0.62 0.90 1.24 2.64 2.95 2.16 2.15 2.49 1.81 0.67 0.56 Average annual rainfall 18.49 San Angelo Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.01 0.00 0.00 0.26 0.05 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 3.65 4.47 5.00 5.10 11.24 6.01 7.21 8.13 11.00 8.68 3.55 3.98 Median 0.58 0.62 0.65 1.29 2.32 2.09 0.70 1.38 2.38 1.90 0.68 0.33 Average 0.79 1.04 0.92 1.66 2.78 2.20 1.10 1.75 2.83 2.24 0.98 0.76 Average annual rainfall 19.12 San Antonio Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.01 0.03 0.02 0.00 0.01 0.00 0.00 0.05 0.00 0.00 0.03 Maximum 8.52 6.43 6.12 9.32 12.85 11.95 8.29 11.14 13.09 17.96 8.51 13.96 Median 1.10 1.85 1.27 1.94 3.04 2.70 1.21 2.00 2.24 2.75 1.93 1.09 Average 1.59 1.92 1.66 2.52 3.97 3.61 1.82 2.45 3.08 3.42 2.24 1.69 Average annual rainfall 29.96 Waco Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.03 0.00 0.04 0.12 0.52 0.27 0.00 0.00 0.00 0.00 0.13 0.04 Maximum 5.92 7.69 5.56 13.37 15.00 12.06 8.58 8.91 7.29 10.51 7.03 9.72 Median 1.55 2.00 2.22 2.76 3.87 2.34 0.82 0.96 2.57 2.37 2.29 1.94 Average 1.83 2.28 2.25 3.30 4.49 2.98 1.82 1.76 3.02 3.12 2.40 2.31 Average annual rainfall 31.68 A9
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Appendix C Case Studies Lady Bird Johnson Wildflower Center Austin 4801 La Crosse Avenue Austin, Texas 78739 (512) 292-4100 http://www.wildflower.org Capacity: 70,000 gallons Catchment area: 17,000 square feet Demand: Gardens and landscaping Harvested rainwater from three separate catchment areas provides 10 to 15 percent of the garden and landscaping irrigation of the Lady Bird Johnson National Wildflower Research Center in Austin. An integral part of its architecture, the Center's rainwater harvesting system serves to not only conserve water, but also as a public education tool. The Center collects water from 17,000 square feet of roof space and can store more than 70,000 gallons in on-site cisterns. One of the most prominent features of the center The entry cistern at the Lady Bird Johnson is the 43-foot native-stone-façade tower cistern, Wildflower Research Center is reminiscent of which is built around a 5,000-gallon storage the stone-and-mortar cisterns used by Hill tank. Metal rooftops totaling an area of 17,000 Country settlers. Water from a 1,200-square- square feet drain into the tower cistern and two foot roof area is conveyed to the entry cistern 25,000-gallon tanks collect a total of about via an aqueduct. 300,000 gallons in an average rainfall year. A pressurized distribution system delivers water from the large tanks to an irrigation system. The municipal water supply is linked to the systems with backflow prevention devices to prevent water contamination. The 3,000-gallon entry cistern, fed by an elevated stone-faced aqueduct draining just less than 1,200 square feet of roof area, is reminiscent of rainwater cisterns used by original Hill Country settlers. The Little House cistern captures rainwater from a roof area of about 700 square feet in the Children’s Area. In addition, the Wetland Pond, the Commons Well, and the Balcony Spring together collect 2,500 gallons per inch of rain from the roofs, although water from these features is not used for irrigation. A11
H-E-B Austin 6900 Brodie Lane (corner William Cannon Blvd. and Brodie Lane) Austin, Texas 78745 Capacity: 28,000 gallons Catchment area: 50,000 square feet Demand: Native and adapted plant landscape Two 8,000-gallon and two 6,000-gallon painted steel tanks are fed from a 24-inch-diameter collection pipe draining the 50,000-square-foot The H-E-B at the corner of Brodie Lane roof. Using efficient drip irrigation, captured and William Cannon Blvd. in south central Austin irrigates an adjacent rainwater irrigates an adjacent water-thrifty landscape of water-thrifty plants with landscape of native and adapted trees and rainwater stored in four painted steel ornamentals. Walkways and plant labels tanks totaling 28,000 gallons. A 24-inch- enhance the attractiveness of the site. diameter pipe conveys water from the roof to the tanks. The four tanks are connected with 6-inch PVC pipes and valves, allowing a tank to be taken off-line to be drained and cleaned. H-E-B, based in San Antonio, prides itself on environmental stewardship in the communities where its supermarkets conduct business. H-E-B saves 6.2 million gallons of water annually by recycling condensation from manufacturing steam equipment. Tanks are linked with 6- inch PVC pipe. Valves allow taking one or more tank off-line for draining or cleaning. A12
Sunset Canyon Pottery Dripping Springs 4002 E. Highway 290 Dripping Springs, Texas 78620 (512) 894-0938 Sunset Canyon Pottery supplies all its potable and pottery works water demand with water stored in a 46,000-gallon ferrocement tank. When visiting this site on private property, please first request permission from Sunset Canyon Pottery staff. The ferrocement tank at Sunset Canyon Pottery supplies process water for pottery works, as well as potable water for the straw-bale studio and gift shop. The tank was constructed first by forming an armature of steel reinforcement bars, then spraying on a cement-like material similar to that used for in-ground swimming pools. A13
New Braunfels Municipal Utility District New Braunfels New Braunfels Utilities Service Center 355 FM 306 New Braunfels, Texas 78130 The New Braunfels Utilities Service Center, completed in 2004, captures rainwater in four 1,000-gallon plastic-lined galvanized steel tanks, one located at each building wing. Water is used to irrigate the landscape of native and adapted plants. The metal tanks form both a practical and aesthetic feature of the architecture of this public building. Four lined, galvanized steel tanks will capture water for irrigation of native and adapted plants. A14
Hays County Cooperative Extension Office San Marcos 1253 Civic Center Loop San Marcos, Texas 78666 (512) 393-2120 Capacity: 750-gallon galvanized metal tank 1,600 polyethylene tank Catchment area: 2,500 square feet Demand: Demonstration garden Cost: $1,125 The Hays County Extension Office captures rainwater from half the roof area of its 5,000-square-foot building As a demonstration project, a 750-gallon galvanized in two tanks: a 750-gallon galvanized steel tank captures rainwater from the 5,000-square- foot roof of the Hays County Extension Office. steel tank and a 1,600-gallon black polypropylene tank using existing guttering and downspouts. Plans are in the works for water to be gravity-fed to an adjacent Master Gardener demonstration garden. A15
Edwards Aquifer Authority San Antonio 1615 N. St. Mary's Street San Antonio, TX 78215 (210) 222-2204 Capacity: 2,500 gallons Catchment area: 1,135 square feet Demand: Landscaping The Edwards Aquifer Authority collects rainwater from a catchment area of 1,135 square feet in two cisterns. Water is delivered through gravity flow into a 500-gallon polypropylene tank in the courtyard area. The second cistern, a 2,000- A 2,000-gallon, ranch-style metal cistern is one of two tanks that capture rainwater for landscaping at the gallon ranch-style metal cistern, is Edwards Aquifer Authority building. (Photo courtesy: located on the front lawn, visible from Lara Stuart) the street. Harvested rainwater is used to irrigate the 266-square-foot courtyard, and 2,700-square-foot lawn. A16
J.M. Auld Lifetime Learning Center Kerrville 1121 Second Street Kerrville, Texas 72028 (830) 257-2218 Capacity: 6,600 gallons (Two 3,300-gallon stacked concrete ring tanks) Catchment area: 5,000 square feet Demand: Adjacent gardens Pondless waterfall Total Cost: $10,500 Breakdown: Two 3,300 concrete tanks, $4,766 Plumbing supplies, $520 Pump, pressure tank, switch, $1,535 Gutter work, $541 Electrical supplies, $160 Trencher rental, $175 In-kind labor, Kerrville ISD, $2,800 Stacked concrete ring 3,000-gallon tank at the Auld Center, Kerrville, The Auld Lifelong Learning Center of Kerrville showing first flush diverter and Independent School District is a community education cistern. facility operated by Kerrville Independent School District. Installed in 2003, two 3,300-gallon stacked concrete-ring tanks collect rainwater from a 5,000-square-foot roof. Tanks are located at the back corners of the building, with a transverse 3-inch PVC pipe conveying the rainwater drained from the front half of the roof. Five-gallon first flush diverters at each corner capture the dust and debris of the initial runoff of each rainfall event. Tanks are fitted with unique water-level sight gages. Vertical rods the same length as the tank height are suspended on floating platforms within the tank. The length of rod protruding from the tops of tanks indicates water level. Captured rainwater will irrigate several adjacent themed gardens. In addition, a unique water feature, a recirculating waterfall, adds aesthetic interest. A17
Menard ISD Elementary School Menard 200 Gay St. Menard, Texas 76859 Container garden and landscape-plant irrigation Capacity: 1,000-gallon green polyethylene tank Catchment area: 600 square feet Demand: 50 emitters: 20 landscape plants, 30 container garden emitters Total cost: $475 Breakdown: Tank, $400 Connections and valves/roofwasher, $35 Using existing gutters and downspouts, Black poly pipe and emitters, rainwater harvesting techniques were used to $40 create a backyard wildscape. The principles of wildscape construction can be transferred to The rainwater harvesting system serves large wildlife management programs. multiple purposes of education, beauty, and habitat improvement at Menard Independent School District Elementary School. The wildscape provides the requirements of food, water, and shelter for native animals. The demonstration site aids in teaching students about healthful wildlife habitats and container and landscape gardening. The water features, gazebo, and rock walkway enhance the outdoor esthetics of the school. A backyard wildscape at Menard Elementary School demonstrates the requirements of food, water, and shelter for rangeland maintenance conducive to supporting wildlife. Using existing gutters and Menard Elementary School rainwater harvesting installation showing downspout, downspouts from the roof of Menard 1,000-gallon poly tank, and gazebo (left) Elementary School, rainwater is diverted into surrounded by native and adapted landscape two 1,000-gallon green polypropylene tanks. plants. In this very attractive installation, One tank supplies a birdbath made of rocks harvested rainwater (using existing gutter and with natural cavities and a prefabricated pond. downspouts) furnishes water not only to the landscape, but also to a watering pond, Both water features are supplied with water birdbath, and wildlife guzzler. (Photo courtesy: conveyed by gravity pressure through 3/4-inch Billy Kniffen) PVC pipe and drip emitters. Native plants provide a food source and cover for wildlife. A18
Walker County Cooperative Extension Office Huntsville 102 Tam Road Huntsville, Texas 77320 (936) 435-2426 Capacity: 550-gallon polyethylene tank Catchment area: 1,500 square feet Demand: Master Gardener demonstration plot Total cost: Total: $230 Breakdown: Used 550-gallon tank, $150 Plumbing supplies and fittings, $70 Glue, thinner, and paint, Rainwater captured from the 1,500-square-foot roof $10 of the Walker County Extension office is stored in a 550-gallon polypropylene tank, a type readily The Walker County Master Gardeners and available at ranch supply retailers. The 10-gallon flush diverter is the vertical standpipe visible to the staff of Texas Cooperative Extension, left of the tank. Captured rainwater irrigates an supervised by agricultural county agent adjacent Master Gardener demonstration garden, Reginald Lepley, installed a rainwater foreground. harvesting system at the Walker County Extension office for a cost of less than $250. A used white 550-gallon polypropylene tank was thoroughly cleaned and pressure- washed, and painted with brown latex paint to discourage algae growth. Raising the tank on concrete blocks allows gravity flow to a 10-foot by 25-foot Master Gardener demonstration garden. A detailed parts list, instructions and tips for rainwater harvesting in general, and more information on this installation can be found at urbantaex.tamu.edu/D9/Walker/AG/HomeHort/WCMG/hortdemo/Waterdemo/index A19
AMD/Spansion FAB25 Austin 5204 E. Ben White Blvd. Austin, Texas 78741 Rainwater drained from the facility’s roofs and groundwater from the building perimeter drains furnish all the water needed for landscape irrigation on AMD’s Spansion site in east Austin. Water is collected and stored in a 10,000-gallon fiberglass tank, and then pressurized through the site irrigation loop using surplus pumps. The water savings has been verified at about 4.75 million gallons per year using online flow meters. In-house engineers designed the system and facilities tradespersons installed the tank, pump, piping, and electricity. The irrigation reclaim system has a three-year return on investment. The plant also has segregated drains that allow the reuse and recycling of rinse water from the wafer manufacturing process for cooling tower and Ultra-pure treatment plant makeup drastically reducing city-supplied water. The water savings from the rinse water reuse system is approximately 210 million gallons per year and had a return on investment of less than one year. A20
J.J. Pickle Elementary School/St. John Community Center Austin Corner of Blessing and Wheatley Avenues Austin, Texas A model of sustainable design and building, the J.J. Pickle Elementary and St. John Community Center in northeast Austin is a joint project of Austin Independent School District and the City of Austin. Water from a portion of the 116,200-square-foot facility drains into three tanks, which provide cooling water to the air-conditioning system. For energy savings, the classrooms, gym, dining area, and City library use sunlight rather than electric lights during the day. The complex opened in January 2002, with operational and maintenance cost savings of $100,000 expected each year. The complex includes a public elementary school, shared gymnasium, a health center, public and school libraries, and a community policing office. The cost of construction is $13.6 million, with the AISD funding about $8.3 million and the Water collected from the roof of the J.J. Pickle City of Austin funding about $5.3 million. Elementary School and St. John Community Center The money came from a 1996 School is stored in three large tanks behind the building and District bond election and a City 1998 used as cooling water for the complex’s air- conditioning system. bond package. A21
Feather & Fur Animal Hospital Austin 9125 Manchaca Road Austin, Texas 78748 Captured water from the roof, parking lot, and condensate from the air conditioners is the sole source irrigation water for a 1- acre turf landscape at the Feather & Fur Animal Hospital in South Austin. Dr. Howard Blatt first explored ways to make use of an existing hand-dug 18,000-gallon underground cistern. The project has since been expanded to take advantage of other rainwater The Feather & Fur Animal Hospital in South Austin features a standing-seam metal roof for rainwater harvesting. sources. Rainwater collected from a standing-seam metal roof gravity flows into the cistern. Then water from the parking lot flows through a water quality pond with gabion for sedimentation and filtration treatment. From the pond, water flows via a 6-inch pipe to catch basin. A small sump pump empties to a 12,500-gallon fiberglass tank. Additionally, the primary condensation line from the air handlers also drains into the gutter and downspout system, which services the roof. A22
Pomerening/Dunford Residence Bexar County The Pomerening/Dunford family lives on the western edge of Bexar County and uses rainwater harvesting for all of their potable needs. The four-year-old installation features two 10,000-gallon cisterns that store captured water from a 2,400-square-foot collection area. Two 10,000-gallon cisterns collect rainwater at the Pomerening/Dunford residence in Bexar County. A23
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Appendix D Tax Exemption Application Form A25

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Texas Guide to Rainwater Harvesting - 2005

  • 1.
    The Texas Manual on Rainwater Harvesting Texas Water Development Board Third Edition
  • 2.
    The Texas Manualon Rainwater Harvesting Texas Water Development Board in cooperation with Chris Brown Consulting Jan Gerston Consulting Stephen Colley/Architecture Dr. Hari J. Krishna, P.E., Contract Manager Third Edition 2005 Austin, Texas
  • 3.
    Acknowledgments The authors wouldlike to thank the following persons for their assistance with the production of this guide: Dr. Hari Krishna, Contract Manager, Texas Water Development Board, and President, American Rainwater Catchment Systems Association (ARCSA); Jen and Paul Radlet, Save the Rain; Richard Heinichen, Tank Town; John Kight, Kendall County Commissioner and Save the Rain board member; Katherine Crawford, Golden Eagle Landscapes; Carolyn Hall, Timbertanks; Dr. Howard Blatt, Feather & Fur Animal Hospital; Dan Wilcox, Advanced Micro Devices; Ron Kreykes, ARCSA board member; Dan Pomerening and Mary Dunford, Bexar County; Billy Kniffen, Menard County Cooperative Extension; Javier Hernandez, Edwards Aquifer Authority; Lara Stuart, CBC; Wendi Kimura, CBC. We also acknowledge the authors of the previous edition of this publication, The Texas Guide to Rainwater Harvesting, Gail Vittori and Wendy Price Todd, AIA. Disclaimer The use of brand names in this publication does not indicate an endorsement by the Texas Water Development Board, or the State of Texas, or any other entity. Views expressed in this report are of the authors and do not necessarily reflect the views of the Texas Water Development Board, or any other entity.
  • 4.
    Table of Contents Chapter1 Introduction..................................................................................................... 1 Chapter 2 Rainwater Harvesting System Components................................................. 5 Basic Components .......................................................................................................... 5 The Catchment Surface................................................................................................... 5 Gutters and Downspouts ................................................................................................. 6 Leaf Screens.................................................................................................................... 7 First-Flush Diverters ....................................................................................................... 8 Roof Washers................................................................................................................ 10 Storage Tanks................................................................................................................ 10 Pressure Tanks and Pumps............................................................................................ 16 Treatment and Disinfection Equipment ........................................................................ 17 Chapter 3 Water Quality and Treatment..................................................................... 21 Considerations for the Rainwater Harvesting System Owner ...................................... 21 Water Quality Standards ............................................................................................... 22 Factors Affecting Water Quality................................................................................... 22 Water Treatment ........................................................................................................... 23 Chapter 4 Water Balance and System Sizing............................................................... 29 How Much Water Can Be Captured? ........................................................................... 29 Rainfall Distribution ..................................................................................................... 30 Calculating Storage Capacity........................................................................................ 32 The Water Balance Method Using Monthly Demand and Supply ............................... 32 Estimating Demand....................................................................................................... 33 Estimating indoor water demand .............................................................................. 33 Indoor water conservation......................................................................................... 35 Estimating outdoor water demand ............................................................................ 36 Chapter 5 Rainwater Harvesting Guidelines ............................................................... 41 RWH Best Management Practices................................................................................ 41 Water Conservation Implementation Task Force Guidelines................................... 41 American Rainwater Catchment Systems Association............................................. 41 Building Codes.............................................................................................................. 41 Cistern Design, Construction, and Capacity ................................................................. 42 Backflow Prevention and Dual-Use Systems ............................................................... 42 Required Rainwater Harvesting Systems...................................................................... 43 Chapter 6 Cost Estimation............................................................................................. 45 Comparing to Other Sources of Water.......................................................................... 51 i
  • 5.
    Chapter 7 Financialand Other Incentives ................................................................... 53 Tax Exemptions ............................................................................................................ 53 Municipal Incentives..................................................................................................... 54 Rainwater Harvesting at State Facilities ....................................................................... 55 Performance Contracting .............................................................................................. 56 Appendix A References ................................................................................................. A1 Appendix B Rainfall Data ............................................................................................. A7 Appendix C Case Studies ............................................................................................ A11 Appendix D Tax Exemption Application Form ........................................................ A25 ii
  • 6.
    Chapter 1 Introduction Rainwater harvesting is an ancient extending their use; rainwater technique enjoying a revival in eliminates the need for a water popularity due to the inherent quality of softener and the salts added during rainwater and interest in reducing the softening process. consumption of treated water. Rainwater is sodium-free, important Rainwater is valued for its purity and for persons on low-sodium diets. softness. It has a nearly neutral pH, and Rainwater is superior for landscape is free from disinfection by-products, irrigation. salts, minerals, and other natural and man-made contaminants. Plants thrive Rainwater harvesting reduces flow to under irrigation with stored rainwater. stormwater drains and also reduces Appliances last longer when free from non-point source pollution. the corrosive or scale effects of hard Rainwater harvesting helps utilities water. Users with potable systems prefer reduce the summer demand peak and the superior taste and cleansing delay expansion of existing water properties of rainwater. treatment plants. Archeological evidence attests to the Rainwater harvesting reduces capture of rainwater as far back as 4,000 consumers’ utility bills. years ago, and the concept of rainwater Perhaps one of the most interesting harvesting in China may date back 6,000 aspects of rainwater harvesting is years. Ruins of cisterns built as early as learning about the methods of capture, 2000 B.C. for storing runoff from storage, and use of this natural resource hillsides for agricultural and domestic at the place it occurs. This natural purposes are still standing in Israel synergy excludes at least a portion of (Gould and Nissen-Petersen, 1999). water use from the water distribution Advantages and benefits of rainwater infrastructure: the centralized treatment harvesting are numerous (Krishna, facility, storage structures, pumps, 2003). mains, and laterals. The water is free; the only cost is for Rainwater harvesting also includes land- collection and use. based systems with man-made landscape The end use of harvested water is features to channel and concentrate located close to the source, rainwater in either storage basins or eliminating the need for complex and planted areas. costly distribution systems. When assessing the health risks of Rainwater provides a water source drinking rainwater, consider the path when groundwater is unacceptable or taken by the raindrop through a unavailable, or it can augment limited watershed into a reservoir, through groundwater supplies. public drinking water treatment and distribution systems to the end user. The zero hardness of rainwater helps Being the universal solvent, water prevent scale on appliances, absorbs contaminants and minerals on its 1
  • 7.
    travels to thereservoir. While in of rainwater. The scope, method, residence in the reservoir, the water can technologies, system complexity, come in contact with all kinds of foreign purpose, and end uses vary from rain materials: oil, animal wastes, chemical barrels for garden irrigation in urban and pharmaceutical wastes, organic areas, to large-scale collection of compounds, industrial outflows, and rainwater for all domestic uses. Some trash. It is the job of the water treatment examples are summarized below: plant to remove harmful contaminants For supplemental irrigation water, the and to kill pathogens. Unfortunately, Wells Branch Municipal Utility when chlorine is used for disinfection, it District in North Austin captures also degrades into disinfection by- rainwater, along with air conditioning products, notably trihalomethanes, condensate, from a new 10,000- which may pose health risks. In contrast, square-foot recreation center into a the raindrop harvested on site will travel 37,000-gallon tank to serve as down a roof via a gutter to a storage irrigation water for a 12-acre tank. Before it can be used for drinking, municipal park with soccer fields and it will be treated by a relatively simple offices. process with equipment that occupies about 9 cubic feet of space. The Lady Bird Johnson Wildflower Research Center in Austin, Texas, Rainwater harvesting can reduce the harvests 300,000 gallons of rainwater volume of storm water, thereby annually from almost 19,000 square lessening the impact on erosion and feet of roof collection area for decreasing the load on storm sewers. irrigation of its native plant Decreasing storm water volume also landscapes. A 6,000-gallon stone helps keep potential storm water cistern and its arching stone aqueduct pollutants, such as pesticides, fertilizers, form the distinctive entry to the and petroleum products, out of rivers research center. and groundwater. The Advanced Micro Devices But along with the independence of semiconductor fabrication plant in rainwater harvesting systems comes the Austin, Texas, does not use utility- inherent responsibility of operation and supplied water for irrigation, saving maintenance. For all systems, this $1.5 million per year by relying on responsibility includes purging the first- captured rainwater and collected flush system, regularly cleaning roof groundwater. washers and tanks, maintaining pumps, and filtering water. For potable systems, Reynolds Metals in Ingleside, Texas, responsibilities include all of the above, uses stormwater captured in and the owner must replace cartridge containment basins as process water filters and maintain disinfection in its metal-processing plant, greatly equipment on schedule, arrange to have offsetting the volume of purchased water tested, and monitor tank levels. water. Rainwater used for drinking should be The city of Columbia, Nuevo León, tested, at a minimum, for pathogens. Mexico, is in the planning stages of Rainwater harvesting, in its essence, is developing rainwater as the basis for the collection, conveyance, and storage the city’s water supply for new 2
  • 8.
    growth areas, withlarge industrial In fact, rainwater harvesting is developments being plumbed for encouraged by Austin and San Antonio storage and catchment. water utilities as a means of conserving On small volcanic or coral islands, water. The State of Texas also offers rainwater harvesting is often the only financial incentives for rainwater option for public water supply, as harvesting systems. Senate Bill 2 of the watersheds are too small to create a 77th Legislature exempts rainwater major river, and groundwater is either harvesting equipment from sales tax, and nonexistent or contaminated with salt allows local governments to exempt water. Bermuda, the U.S. Virgin rainwater harvesting systems from ad Islands, and other Caribbean islands valorem (property) taxes. require cisterns to be included with all Rainwater harvesting systems can be as new construction. simple as a rain barrel for garden In Central Texas, more than 400 full- irrigation at the end of a downspout, or scale rainwater harvesting systems have as complex as a domestic potable system been installed by professional or a multiple end-use system at a large companies, and more than 6,000 rain corporate campus. barrels have been installed through the Rainwater harvesting is practical only City of Austin’s incentive program in the when the volume and frequency of past decade. Countless “do-it- rainfall and size of the catchment surface yourselfers” have installed systems over can generate sufficient water for the the same time period. intended purpose. An estimated 100,000 residential From a financial perspective, the rainwater harvesting systems are in use installation and maintenance costs of a in the United States and its territories rainwater harvesting system for potable (Lye, 2002). More are being installed by water cannot compete with water the urban home gardener seeking supplied by a central utility, but is often healthier plants, the weekend cabin cost-competitive with installation of a owner, and the homeowner intent upon well in rural settings. the “green” building practices – all With a very large catchment surface, seeking a sustainable, high-quality water such as that of big commercial building, source. Rainwater harvesting is also the volume of rainwater, when captured recognized as an important water- and stored, can cost-effectively serve conserving measure, and is best several end uses, such as landscape implemented in conjunction with other irrigation and toilet flushing. efficiency measures in and outside of the home. Some commercial and industrial buildings augment rainwater with Harvested rainwater may also help some condensate from air conditioning Texas communities close the gap systems. During hot, humid months, between supply and demand projected warm, moisture-laden air passing over by the Texas Water Development Board the cooling coils of a residential air (TWDB), as the state’s population nearly conditioner can produce 10 or more doubles between 2000 and 2050 (Texas gallons per day of water. Industrial Water Development Board, 2002). facilities produce thousands of gallons 3
  • 9.
    per day ofcondensate. An advantage of References condensate capture is that its maximum Gould J, Nissen-Petersen E. 1999. production occurs during the hottest Rainwater catchment systems for month of the year, when irrigation need domestic rain: design construction is greatest. Most systems pipe and implementation. London: condensate into the rainwater cistern for Intermediate Technology storage. Publications. 335 p. The depletion of groundwater sources, Krishna H. 2003. An overview of the poor quality of some groundwater, rainwater harvesting systems and high tap fees for isolated properties, the guidelines in the United States. flexibility of rainwater harvesting Proceedings of the First American systems, and modern methods of Rainwater Harvesting Conference; treatment provide excellent reasons to 2003 Aug 21-23; Austin (TX). harvest rainwater for domestic use. Lye D. 2002. Health risks associated The scope of this manual is to serve as a with consumption of untreated water primer in the basics of residential and from household roof catchment small-scale commercial rainwater systems. Journal of the American harvesting systems design. It is intended Water Resources Association to serve as a first step in thinking about 38(5):1301-1306. options for implementing rainwater harvesting systems, as well as Texas Water Development Board. 2002. advantages and constraints. Water for Texas – 2002. Austin (TX): Texas Water Development Board. 155 p. 4
  • 10.
    Chapter 2 Rainwater Harvesting System Components Rainwater harvesting is the capture, building code officer should be diversion, and storage of rainwater for a consulted concerning safe, sanitary number of different purposes including operations and construction of these landscape irrigation, drinking and systems. domestic use, aquifer recharge, and stormwater abatement. Basic Components In a residential or small-scale Regardless of the complexity of the application, rainwater harvesting can be system, the domestic rainwater as simple as channeling rain running off harvesting system (Figure 2-1) an unguttered roof to a planted landscape comprises six basic components: area via contoured landscape. To prevent Catchment surface: the collection erosion on sloped surfaces, a bermed surface from which rainfall runs off concave holding area down slope can Gutters and downspouts: channel store water for direct use by turfgrass or water from the roof to the tank plants (Waterfall, 1998). More complex systems include gutters, pipes, storage Leaf screens, first-flush diverters, and tanks or cisterns, filtering, pump(s), and roof washers: components which water treatment for potable use. remove debris and dust from the captured rainwater before it goes to This chapter focuses on residential or the tank small-scale commercial systems, for both irrigation and potable use. One or more storage tanks, also called cisterns The local health department and city Delivery system: gravity-fed or pumped to the end use Treatment/purification: for potable systems, filters and other methods to make the water safe to drink The Catchment Surface The roof of a building or house is the obvious first choice for catchment. For additional capacity, an open-sided barn – called a rain barn or pole barn – can be built. Water tanks and other rainwater system equipment, such as pumps and filters, as well as vehicles, bicycles, and gardening tools, can be stored under the barn. Water quality from different roof Figure 2-1. Typical rainwater harvesting catchments is a function of the type of installation roof material, climatic conditions, and 5
  • 11.
    the surrounding environment harvested is usually suitable only for (Vasudevan, 2002). irrigation due to leaching of compounds. Metal Slate. Slate’s smoothness makes it ideal The quantity of rainwater that can be for a catchment surface for potable use, collected from a roof is in part a function assuming no toxic sealant is used; of the roof texture: the smoother the however, cost considerations may better. A commonly used roofing preclude its use. material for rainwater harvesting is sold under the trade name Galvalume®, a 55 Gutters and Downspouts percent aluminum/45 percent zinc alloy- Gutters are installed to capture rainwater coated sheet steel. Galvalume® is also running off the eaves of a building. available with a baked enamel coating, Some gutter installers can provide or it can be painted with epoxy paint. continuous or seamless gutters. Some caution should be exercised For potable water systems, lead cannot regarding roof components. Roofs with be used as gutter solder, as is sometimes copper flashings can cause discoloration the case in older metal gutters. The of porcelain fixtures. slightly acidic quality of rain could dissolve lead and thus contaminate the Clay/concrete tile water supply. Clay and concrete tiles are both porous. The most common materials for gutters Easily available materials are suitable and downspouts are half-round PVC, for potable or nonpotable systems, but vinyl, pipe, seamless aluminum, and may contribute to as much as a 10- galvanized steel. percent loss due to texture, inefficient flow, or evaporation. To reduce water Seamless aluminum gutters are usually loss, tiles can be painted or coated with a installed by professionals, and, therefore, sealant. There is some chance of toxins are more expensive than other options. leaching from the tile sealant or paint, Regardless of material, other necessary but this roof surface is safer when components in addition to the horizontal painted with a special sealant or paint to gutters are the drop outlet, which routes prevent bacterial growth on porous water from the gutters downward and at materials. least two 45-degree elbows which allow Composite or asphalt shingle the downspout pipe to snug to the side of Due to leaching of toxins, composite the house. Additional components shingles are not appropriate for potable include the hardware, brackets, and systems, but can be used to collect water straps to fasten the gutters and for irrigation. Composite roofs have an downspout to the fascia and the wall. approximated 10-percent loss due to Gutter Sizing and Installation inefficient flow or evaporation (Radlet When using the roof of a house as a and Radlet, 2004). catchment surface, it is important to Others consider that many roofs consist of one Wood shingle, tar, and gravel. These or more roof “valleys.” A roof valley roofing materials are rare, and the water occurs where two roof planes meet. This is most common and easy to visualize 6
  • 12.
    when considering ahouse plan with an both before and after the storage tank. “L” or “T” configuration. A roof valley The defense in keeping debris out of a concentrates rainfall runoff from two rainwater harvesting system is some type roof planes before the collected rain of leaf screen along the gutter or in the reaches a gutter. Depending on the size downspout. of roof areas terminating in a roof valley, Depending upon the amount and type of the slope of the roofs, and the intensity tree litter and dust accumulation, the of rainfall, the portion of gutter located homeowner may have to experiment to where the valley water leaves the eave of find the method that works best. Leaf the roof may not be able to capture all screens must be regularly cleaned to be the water at that point, resulting in effective. If not maintained, leaf screens spillage or overrunning. can become clogged and prevent Besides the presence of one or more roof rainwater from flowing into a tank. valleys, other factors that may result in Built-up debris can also harbor bacteria overrunning of gutters include an and the products of leaf decay. inadequate number of downspouts, Leaf guards are usually ¼-inch mesh excessively long roof distances from screens in wire frames that fit along the ridge to eave, steep roof slopes, and length of the gutter. Leaf guards/screens inadequate gutter maintenance. are usually necessary only in locations Variables such as these make any gutter with tree overhang. Guards with profiles sizing rules of thumb difficult to apply. conducive to allowing leaf litter to slide Consult you gutter supplier about your off are also available. situation with special attention to determine where gutter overrunning The funnel-type downspout filter is areas may occur. At these points along made of PVC or galvanized steel fitted an eave, apply strategies to minimize with a stainless steel or brass screen. possible overrunning to improve This type of filter offers the advantage of catchment efficiency. Preventative easy accessibility for cleaning. The strategies may include modifications to funnel is cut into the downspout pipe at the size and configuration of gutters and the same height or slightly higher than addition of gutter boxes with the highest water level in the storage downspouts and roof diverters near the tank. eave edge. Strainer baskets are spherical cage-like Gutters should be installed with slope strainers that slip into the drop outlet of towards the downspout; also the outside the downspout. face of the gutter should be lower than A cylinder of rolled screen inserted into the inside face to encourage drainage the drop outlet serves as another method away from the building wall. of filtering debris. The homeowner may need to experiment with various grid Leaf Screens sizes, from insect screen to hardware To remove debris that gathers on the cloth. catchment surface, and ensure high quality water for either potable use or to Filter socks of nylon mesh can be work well without clogging irrigation installed on the PVC pipe at the tank emitters, a series of filters are necessary. inflow. Essentially, mesh screens remove debris 7
  • 13.
    First-Flush Diverters A preliminary study by Rain Water A roof can be a natural collection Harvesting and Waste Water Systems surface for dust, leaves, blooms, twigs, Pty Ltd., a rainwater harvesting insect bodies, animal feces, pesticides, component vendor in Australia, and other airborne residues. The first- recommends that between 13 and 49 flush diverter routes the first flow of gallons be diverted per 1,000 square feet. water from the catchment surface away The primary reason for the wide from the storage tank. The flushed water variation in estimates is that there is no can be routed to a planted area. While exact calculation to determine how much leaf screens remove the larger debris, initial water needs to be diverted because such as leaves, twigs, and blooms that there are many variables that would fall on the roof, the first-flush diverter determine the effectiveness of washing gives the system a chance to rid itself of the contaminants off the collection the smaller contaminants, such as dust, surface, just as there are many variables pollen, and bird and rodent feces. determining the make up of the The simplest first-flush diverter is a PVC contaminants themselves. For example, standpipe (Figure 2-2). The standpipe the slope and smoothness of the fills with water first during a rainfall collection surface, the intensity of the event; the balance of water is routed to rain event, the length of time between the tank. The standpipe is drained events (which adds to the amount of continuously via a pinhole or by leaving accumulated contaminants), and the the screw closure slightly loose. In any nature of the contaminants themselves case, cleaning of the standpipe is add to the difficulty of determining just accomplished by removing the PVC how much rain should be diverted during cover with a wrench and removing first flush. In order to effectively wash a collected debris after each rainfall event. collection surface, a rain intensity of one-tenth of an inch of rain per hour is There are several other types of first- needed to wash a sloped roof. A flat or flush diverters. The ball valve type near-flat collection surface requires 0.18 consists of a floating ball that seals off inches of rain per hour for an effective the top of the diverter pipe (Figure 2-3) washing of the surface. when the pipe files with water. The recommended diversion of first Opinions vary on the volume of flush ranges from one to two gallons of rainwater to divert. The number of dry first-flush diversion for each 100 square days, amount of debris, and roof surface feet of collection area. If using a roof for are all variables to consider. a collection area that drains into gutters, One rule of thumb for first-flush calculate the amount of rainfall area that diversion is to divert a minimum of 10 will be drained into every gutter feeding gallons for every 1,000 square feet of your system. Remember to calculate the collection surface. However, first-flush horizontal equivalent of the “roof volumes vary with the amount of dust on footprint” when calculating your the roof surface, which is a function of catchment area. (Please refer to the the number of dry days, the amount and Figure 4-1 in Chapter 4, Water Balance type of debris, tree overhang, and and System Sizing.) If a gutter receives season. the quantity of runoff that require multiple downspouts, first-flush 8
  • 14.
    First-Flush Diverters Standpipe The simplest first-flush diverter is a 6- or 8-inch PVC standpipe (Figure 2-2). The diverter fills with water first, backs up, and then allows water to flow into the main collection piping. These standpipes usually have a cleanout fitting at the bottom, and must be emptied and cleaned out after each rainfall event. The water from the standpipe may be routed to a planted area. A pinhole drilled at the bottom of the pipe or a hose bibb fixture left slightly open (shown) allows water to gradually leak out. If you are using 3” diameter PVC or similar pipe, allow 33” length of pipe per gallon; 4” diameter pipe needs only 18” of length per gallon; and a little over 8” of 6” diameter pipe is needed to catch a gallon of water. Figure 2-2. Standpipe first-flush diverter Standpipe with ball valve The standpipe with ball valve is a variation of the standpipe filter. The cutaway drawing (Figure 2-3) shows the ball valve. As the chamber fills, the ball floats up and seals on the seat, trapping first-flush water and routing the balance of the water to the tank. Figure 2-3. Standpipe with ball valve 9
  • 15.
    diversion devices willbe required for (handling rainwater from 1,500- and each downspout. 3,500-square-foot catchments, respectively). The box is placed atop a Roof Washers ladder-like stand beside the tank, from The roof washer, placed just ahead of the which the system owner accesses the storage tank, filters small debris for box for cleaning via the ladder. In potable systems and also for systems locations with limited drop, a filter with using drip irrigation. Roof washers the canisters oriented horizontally is consist of a tank, usually between 30- indicated, with the inlet and outlet of the and 50-gallon capacity, with leaf filter being nearly parallel. strainers and a filter (Figure 2-4). One commercially available roof washer has Storage Tanks a 30-micron filter. (A micron, also called The storage tank is the most expensive a micrometer, is one-millionth of a component of the rainwater harvesting meter. A 30-micron filter has pores system. about one-third the diameter of a human The size of storage tank or cistern is hair.) dictated by several variables: the All roof washers must be cleaned. rainwater supply (local precipitation), Without proper maintenance they not the demand, the projected length of dry only become clogged and restrict the spells without rain, the catchment flow of rainwater, but may themselves surface area, aesthetics, personal become breeding grounds for pathogens. preference, and budget. The box roof washer (Figure 2-4) is a A myriad of variations on storage tanks commercially available component and cisterns have been used over the consisting of a fiberglass box with one centuries and in different geographical or two 30-micron canister filters regions: earthenware cisterns in pre- biblical times, large pottery containers in Africa, above-ground vinyl-lined swimming pools in Hawaii, concrete or brick cisterns in the central United States, and, common to old homesteads in Texas, galvanized steel tanks and attractive site-built stone-and-mortar cisterns. For purposes of practicality, this manual will focus on the most common, easily installed, and readily available storage options in Texas, some still functional after a century of use. Storage tank basics Storage tanks must be opaque, either upon purchase or painted later, to Figure 2-4. Box roof washer inhibit algae growth. 10
  • 16.
    For potable systems,storage tanks truck, preferably near a driveway or must never have been used to store roadway. toxic materials. Water weighs just over 8 pounds per Tanks must be covered and vents gallon, so even a relatively small 1,500- screened to discourage mosquito gallon tank will weigh 12,400 pounds. A breeding. leaning tank may collapse; therefore, Tanks used for potable systems must tanks should be placed on a stable, level be accessible for cleaning. pad. If the bed consists of a stable substrate, such as caliche, a load of sand Storage tank siting or pea gravel covering the bed may be Tanks should be located as close to sufficient preparation. In some areas, supply and demand points as possible to sand or pea gravel over well-compacted reduce the distance water is conveyed. soil may be sufficient for a small tank. Storage tanks should be protected from Otherwise, a concrete pad should be direct sunlight, if possible. To ease the constructed. When the condition of the load on the pump, tanks should be soil is unknown, enlisting the services of placed as high as practicable. Of course, a structural engineer may be in order to the tank inlet must be lower than the ensure the stability of the soil supporting lowest downspout from the catchment the full cistern weight. area. To compensate for friction losses in the trunk line, a difference of a couple Another consideration is protecting the of feet is preferable. When converting pad from being undermined by either from well water, or if using a well normal erosion or from the tank backup, siting the tanks near the well overflow. The tank should be positioned house facilitates the use of existing such that runoff from other parts of the plumbing. property or from the tank overflow will not undermine the pad. The pad or bed Water runoff should not enter septic should be checked after intense rainfall system drainfields, and any tank events. overflow and drainage should be routed so that it does not affect the foundation Fiberglass of the tanks or any other structures Fiberglass tanks (Figure 2-5) are built in (Macomber, 2001). standard capacities from 50 gallons to Texas does not have specific rules 15,000 gallons and in both vertical concerning protection of rainwater systems from possible contamination sources; however, to ensure a safe water supply, underground tanks should be located at least 50 feet away from animal stables or above-ground application of treated wastewater. Also, runoff from tank overflow should not enter septic system drainfields. If supplemental hauled water might be needed, tank placement should also take into Figure 2-5. Two 10,000-gallon fiberglass consideration accessibility by a water tanks 11
  • 17.
    cylinder and low-horizontalcylinder Polypropylene tanks do not retain paint configurations. well, so it is necessary to find off-the- shelf tanks manufactured with opaque Fiberglass tanks under 1,000 gallons are plastic. The fittings of these tanks are expensive for their capacity, so aftermarket modifications. Although polypropylene might be preferred. Tanks easy to plumb, the bulkhead fittings for potable use should have a USDA- might be subject to leakage. approved food-grade resin lining and the tank should be opaque to inhibit algae Wood growth. For aesthetic appeal, a wood tank The durability of fiberglass tanks has (Figure 2-7) is often a highly desirable been tested and proven, weathering the choice for urban and suburban rainwater elements for years in Texas oil fields. harvesters. They are easily repaired. Wood tanks, similar to wood water The fittings on fiberglass tanks are an towers at railroad depots, were integral part of the tank, eliminating the historically made of redwood. Modern potential problem of leaking from an wood tanks are usually of pine, cedar, or aftermarket fitting. cypress wrapped with steel tension cables, and lined with plastic. For Polypropylene potable use, a food-grade liner must be Polypropylene tanks (Figure 2-6) are used. commonly sold at farm and ranch supply retailers for all manner of storage uses. Standard tanks must be installed above ground. For buried installation, specially reinforced tanks are necessary to withstand soil expansion and contraction. They are relatively inexpensive and durable, lightweight, and long lasting. Polypropylene tanks are available in capacities from 50 gallons to 10,000 gallons. Figure 2-7. Installation of a 25,000-gallon Timbertank in Central Texas showing the aesthetic appeal of these wooden tanks These tanks are available in capacities from 700 to 37,000 gallons, and are site- built by skilled technicians. They can be dismantled and reassembled at a different location. Figure 2-6. Low-profile 5,000-gallon polypropylene tanks 12
  • 18.
    Metal constructed of stacked rings with sealant Galvanized sheet metal tanks (Figure 2- around the joints. Other types of 8) are also an attractive option for the prefabricated concrete tanks include new urban or suburban garden. They are septic tanks, conduit stood on end, and available in sizes from 150 to 2,500 concrete blocks. These tanks are gallons, and are lightweight and easy to fabricated off-site and dropped into relocate. Tanks can be lined for potable place. use. Most tanks are corrugated galvanized steel dipped in hot zinc for Concrete may be prone to cracking and corrosion resistance. They are lined with leaking, especially in underground tanks a food-grade liner, usually polyethylene in clay soil. Leaks can be easily repaired or PVC, or coated on the inside with although the tank may need to be epoxy paint. The paint, which also drained to make the repair. Involving the extends the life of the metal, must be expertise of a structural engineer to FDA- and NSF-approved for potability. determine the size and spacing of reinforcing steel to match the structural loads of a poured-in-place concrete cistern is highly recommended. A product that repairs leaks in concrete tanks, Xypex™, is now also available and approved for potable use. Figure 2-8. Galvanized sheet metal tanks are usually fitted with a food-grade plastic liner. Concrete Concrete tanks are either poured in place or prefabricated (Figure 2-9). They can be constructed above ground or below ground. Poured-in-place tanks can be Figure 2-9. Concrete tank fabricated from stacking rings of concrete integrated into new construction under a patio, or a basement, and their placement One possible advantage of concrete is considered permanent. tanks is a desirable taste imparted to the A type of concrete tank familiar to water by calcium in the concrete being residents of the Texas Hill Country is dissolved by the slightly acidic 13
  • 19.
    rainwater. For potablesystems, it is Ferrocement structures (Figure 2-10) essential that the interior of the tank be have commonly been used for water plastered with a high-quality material storage construction in developing approved for potable use. countries due to low cost and availability of materials. Small cracks and leaks can Ferrocement easily be repaired with a mixture of Ferrocement is a low-cost steel and cement and water, which is applied mortar composite material. For purposes where wet spots appear on the tank’s of this manual, GuniteTM and ShotcreteTM exterior. Because walls can be as thin as type will be classified as ferrocements. 1 inch, a ferrocement tank uses less Both involve application of the concrete material than concrete tanks, and thus and mortar under pressure from a gun. can be less expensive. As with poured- Gunite, the dry-gun spray method in in-place concrete construction, which the dry mortar is mixed with assistance from a structural engineer is water at the nozzle, is familiar for its use encouraged. in swimming pool construction. Shotcrete uses a similar application, but In-ground polypropylene the mixture is a prepared slurry. Both In-ground tanks are more costly to install methods are cost-effective for larger for two reasons: the cost of excavation storage tanks. Tanks made of Gunite and and the cost of a more heavily reinforced Shotcrete consist of an armature made tank needed if the tank is to be buried from a grid of steel reinforcing rods tied more than 2-feet deep in well-drained together with wire around which is soils. Burying a tank in clay is not placed a wire form with closely spaced recommended because of the layers of mesh, such as expanded metal expansion/contraction cycles of clay lath. A concrete-sand-water mixture is soil. For deeper installation, the walls of applied over the form and allowed to poly tanks must be manufactured thicker cure. It is important to ensure that the and sometimes an interior bracing ferrocement mix does not contain any structure must be added. Tanks are toxic constituents. Some sources buried for aesthetic or space-saving recommend painting above-ground tanks reasons. white to reflect the sun’s rays, reduce Table 2-1 provides some values to assist evaporation, and keep the water cool. in planning an appropriate-sized pad and cistern to meet your water needs and your available space. Many owners of rainwater harvesting systems use multiple smaller tanks in sequence to meet their storage capacity needs. This has the advantage of allowing the owner to empty a tank in order to perform maintenance on one tank at a time without losing all water in storage. A summary of cistern materials, their Figure 2-10. Ferrocement tanks, such as this features, and some words of caution are one, are built in place using a metal armature provided in Table 2-2 to assist the and a sprayed-on cement. prospective harvester in choosing the 14
  • 20.
    appropriate cistern type.Prior to making rainwater installer is recommended to your final selection, consulting with an ensure the right choice for your architect, engineer, or professional situation. Table 2-1. Round Cistern Capacity (Gallons) Height (feet) 6-foot Diameter 12-foot Diameter 18-foot Diameter 6 1,269 5,076 11,421 8 1,692 6,768 15,227 10 2,115 8,460 19,034 12 2,538 10,152 22,841 14 2,961 11,844 26,648 16 3,384 13,535 30,455 18 3,807 15,227 34,262 20 4,230 16,919 38,069 Rain barrel barrel to a second barrel. A screen trap at One of the simplest rainwater the water entry point discourages installations, and a practical choice for mosquito breeding. A food-grade plastic urban dwellers, is the 50- to 75-gallon barrel used for bulk liquid storage in drum used as a rain barrel for irrigation restaurants and grocery stores can be of plant beds. Some commercially fitted with a bulkhead fitting and spigot available rain barrels are manufactured for garden watering. Other options with overflow ports linking the primary include a submersible pump or jet pump. 15
  • 21.
    Table 2-2. CisternTypes MATERIAL FEATURES CAUTION Plastics Trash cans (20-50 gallon) commercially available; use only new cans inexpensive Fiberglass commercially available; must be sited on smooth, solid, alterable and moveable level footing Polyethylene/polypropylene commercially available; UV-degradable, must be alterable and moveable painted or tinted Metals Steel drums (55-gallon) commercially available; verify prior to use for toxics; alterable and moveable prone to corrosion an rust; Galvanized steel tanks commercially available; possibly corrosion and rust; alterable and moveable must be lined for potable use Concrete and Masonry Ferrocement durable and immoveable potential to crack and fail Stone, concrete block durable and immoveable difficult to maintain Monolithic/Poured-in-place durable and immoveable potential to crack Wood Redwood, fir, cypress attractive, durable, can be expensive disassembled and moved Adapted from Texas Guide to Rainwater Harvesting, Second Edition, Texas Water Development Board, 1997. clothes washers, dishwashers, hot-water- Pressure Tanks and Pumps on-demand water heaters – require 20– The laws of physics and the topography 30 psi for proper operation. Even some of most homesteads usually demand a drip irrigation system need 20 psi for pump and pressure tank between water proper irrigation. Water gains 1 psi of storage and treatment, and the house or pressure for every 2.31 feet of vertical end use. Standard municipal water rise. So for gravity flow through a 1-inch pressure is 40 pounds per square inch pipe at 40 psi, the storage tanks would (psi) to 60 psi. Many home appliances – 16
  • 22.
    have to bemore than 90 feet above the house. Since this elevation separation is rarely practical or even desirable, two ways to achieve proper household water pressure are (1) a pump, pressure tank, pressure switch, and check valve (familiar to well owners), or (2) an on-demand pump. Pumps are designed to push water rather than to pull it. Therefore, the system should be designed with the pumps at the same level and as close to the storage tanks as possible. Pump systems draw water from the storage tanks, pressurize it, and store it in a pressure tank until needed. The typical pump-and-pressure tank Figure 2-11. Cistern float filter arrangement consists of a ¾- or 1- horsepower pump, usually a shallow flexible hose, draws water through the well jet pump or a multistage centrifugal filter. pump, the check valve, and pressure switch. A one-way check valve between On-demand pump the storage tank and the pump prevents The new on-demand pumps eliminate pressurized water from being returned to the need for a pressure tank. These the tank. The pressure switch regulates pumps combine a pump, motor, operation of the pressure tank. The controller, check valve, and pressure pressure tank, with a typical capacity of tank function all in one unit. They are 40 gallons, maintains pressure self-priming and are built with a check throughout the system. When the valve incorporated into the suction port. pressure tank reaches a preset threshold, Figure 2-12 shows a typical installation the pressure switch cuts off power to the of an on-demand pump and a 5-micron pump. When there is demand from the fiber filter, 3-micron activated charcoal household, the pressure switch detects filter, and an ultraviolet lamp. Unlike the drop in pressure in the tank and conventional pumps, on-demand pumps activates the pump, drawing more water are designed to activate in response to a into the pressure tank. demand, eliminating the need, cost, and space of a pressure tank. In addition, The cistern float filter (Figure 2-11) some on-demand pumps are specifically allows the pump to draw water from the designed to be used with rainwater. storage tank from between 10 and 16 inches below the surface. Water at this Treatment and Disinfection level is cleaner and fresher than water Equipment closer to the bottom of the tank. The device has a 60-micron filter. An For a nonpotable system used for hose external suction pump, connected via a irrigation, if tree overhang is present, leaf screens on gutters and a roof washer 17
  • 23.
    diverting 10 gallonsfor every 1,000 square feet of roof is sufficient. If drip irrigation is planned, however, sediment filtration may be necessary to prevent clogging of emitters. As standards differ, the drip irrigation manufacturer or vendor should be contacted regarding filtering of water. For potable water systems, treatment beyond the leaf screen and roof washer is necessary to remove sediment and disease-causing pathogens from stored water. Treatment generally consists of filtration and disinfection processes in series before distribution to ensure health and safety. Cartridge Filters and Ultraviolet (UV) Light The most popular disinfection array in Figure 2-12. Typical treatment installation of Texas is two in-line sediment filters – an on-demand pump, 5-micron fiber filter, 3- the 5-micron fiber cartridge filter micron activated charcoal filter, and an followed by the 3-micron activated ultraviolet lamp (top). charcoal cartridge filter – followed by ultraviolet light. This disinfection set-up another cartridge. The ultraviolet (UV) is placed after the pressure tank or after light must be rated to accommodate the the on-demand pump. increased flow. It is important to note that cartridge NSF International (National Sanitation filters must be replaced regularly. Foundation) is an independent testing Otherwise, the filters can actually harbor and certification organization. Filter bacteria and their food supply. The 5- performance can be researched using a micron filter mechanically removes simple search feature by model or suspended particles and dust. The 3- manufacturer on the NSF website. (See micron filter mechanically traps References.) It is best to purchase NSF- microscopic particles while smaller certified equipment. organic molecules are absorbed by the Maintenance of the UV light involves activated surface. In theory, activated cleaning of the quartz sleeve. Many UV charcoal can absorb objectionable odors lights are designed with an integral and tastes, and even some protozoa and wiper unit. Manual cleaning of the cysts (Macomber, 2001). sleeve is not recommended due to the Filters can be arrayed in parallel for possibility of breakage. greater water flow. In other words, two UV lamps are rated in gallons per 5-micron fiber filters can be stacked in minute. For single 5-micron and 3- one large cartridge followed by two 3- micron in-line filters, a UV light rated at micron activated charcoal filters in 12 gallons per minute is sufficient. For 18
  • 24.
    filters in parallelinstallation, a UV light water, referred to as “brine,” containing rated for a higher flow is needed. In-line a concentrate of the contaminants flow restrictors can match flow to the filtered from the feed water, is UV light rating. discharged. The amount of reject water, however, is directly proportional to the UV lights must be replaced after a purity of the feed water. Rainwater, as a maximum of 10,000 hours of operation. purer water source to begin with, would Some lights come with alarms warning generate less brine. Reverse osmosis of diminished intensity. membranes must be changed before they Ozone are fouled by contaminants. Chemically, ozone is O3: essentially a Reverse osmosis (RO) equipment for more reactive form of molecular oxygen household use is commercially available made up of three atoms of oxygen. from home improvement stores such as Ozone acts as a powerful oxidizing agent Lowe’s and Home Depot. to reduce color, to eliminate foul odors, and to reduce total organic carbon in Chlorination water. For disinfection purposes, an For those choosing to disinfect with ozone generator forces ozone into chlorine, automatic self-dosing systems storage tanks through rings or a diffuser are available. A chlorine pump injects stone. Ozone is unstable and reacts chlorine into the water as it enters the quickly to revert to O2 and dissipates house. In this system, appropriate through the atmosphere within 15 contact time is critical to kill bacteria. A minutes. practical chlorine contact time is usually from 2 minutes to 5 minutes with a free A rainwater harvesting system owner in chlorine residual of 2 parts per million Fort Worth uses an ozone generator to (ppm). The time length is based on water keep the water in his 25,000 gallons of pH, temperature, and amount of bacteria. storage “fresh” by circulating ozone Contact time increases with pH and through the five tanks at night. A decreases with temperature. K values standard sprinkler controller switches the (contact times) are shown in Table 3-3. ozone feed from tank to tank. Membrane Filtration (Reverse References Osmosis and Nanofiltration) Membrane filtration, such as reverse Macomber P. 2001. Guidelines on osmosis and nanofiltration work by rainwater catchment systems for forcing water under high pressure Hawaii. Manoa (HI): College of through a semipermeable membrane to Tropical Agriculture and Human filter dissolved solids and salts, both of Resources, University of Hawaii at which are in very low concentrations in Manoa. 51 p. rainwater. Membrane processes, NSF International, filter performance, however, have been known empirically www.nsf.org/certified/DWTU/ to produce “sweeter” water, perhaps by filtering out dissolved metals from Radlet J, Radlet P. 2004. Rainwater plumbing. harvesting design and installation workshop. Boerne (TX): Save the A certain amount of feed water is lost in Rain. any membrane filtration process. Reject 19
  • 25.
    Rain Water Harvestingand Waste Water collected from rooftops in Bryan and Systems Pty Ltd., College Station, Texas [master www.rainharvesting.com.au thesis]. College Station (TX): Texas A&M University. 180 p. Texas Water Development Board. 1997. Texas guide to rainwater harvesting. Waterfall P. 1998. Harvesting rainwater Austin (TX): Texas Water for landscape use. Tucson (AZ): The Development Board. 58 p. University of Arizona College of Agriculture and Life Sciences. 39 p. Vasudevan L. 2002. A study of biological contaminants in rainwater 20
  • 26.
    Chapter 3 Water Quality and Treatment The raindrop as it falls from the cloud is ranges of 100 ppm to more than 800 soft, and is among the cleanest of water ppm. sources. Use of captured rainwater offers The sodium content of some municipal several advantages. water ranges from 10 parts per million Rainwater is sodium-free, a benefit for (ppm) to as high as 250 ppm. Rainwater persons on restricted sodium diets. intended solely for outdoor irrigation may need no treatment at all except for a Irrigation with captured rainwater screen between the catchment surface promotes healthy plant growth. Also, and downspout to keep debris out of the being soft water, rainwater extends the tank, and, if the tank is to supply a drip life of appliances as it does not form irrigation system, a small-pore filter at scale or mineral deposits. the tank outlet to keep emitters from The environment, the catchment surface, clogging. and the storage tanks affect the quality of harvested rainwater. With minimal Considerations for the Rainwater treatment and adequate care of the Harvesting System Owner system, however, rainfall can be used as It is worth noting that owners of potable water, as well as for irrigation. rainwater harvesting systems who supply The falling raindrop acquires slight all domestic needs essentially become acidity as it dissolves carbon dioxide and owners of their “water supply systems,” nitrogen. Contaminants captured by the responsible for routine maintenance, rain from the catchment surface and including filter and lamp replacement, storage tanks are of concern for those leak repair, monitoring of water quality, intending to use rainwater as their and system upgrades. potable water source. The catchment The rainwater harvesting system owner area may have dust, dirt, fecal matter is responsible for both water supply and from birds and small animals, and plant water quality. Maintenance of a debris such as leaves and twigs. rainwater harvesting system is an Rainwater intended for domestic potable ongoing periodic duty, to include: use must be treated using appropriate filtration and disinfection equipment, monitoring tank levels, discussed in Chapter 2, Rainwater cleaning gutters and first-flush Harvesting System Components. devices, repairing leaks, Total dissolved solids (TDS) in repairing and maintaining the system, rainwater, originating from particulate and matter suspended in the atmosphere, adopting efficient water use practices. range from 2 milligrams per liter (mg/l or ppm)1 to 20 mg/l across Texas, compared with municipal water TDS In addition, owners of potable systems must adopt a regimen of: 1 changing out filters regularly, For dilute aqueous solutions mg/l is approximately equal to ppm because a liter of water weighs one kilogram. 21
  • 27.
    maintaining disinfection equipment, the state, acid rain is not considered a such as cleaning and replacing serious concern in Texas. ultraviolet lamps, and regularly testing water quality. Particulate matter Particulate matter refers to smoke, dust, Water Quality Standards and soot suspended in the air. Fine No federal or state standards exist particulates can be emitted by industrial currently for harvested rainwater quality, and residential combustion, vehicle although state standards may be exhaust, agricultural controlled burns, developed in 2006. and sandstorms. As rainwater falls through the atmosphere, it can The latest list of drinking water incorporate these contaminants. requirements can be found on the United States Environmental Protection Particulate matter is generally not a Agency’s website. (See References.) The concern for rainwater harvesting in next section discusses the potential Texas. However, if you wish, geographic vectors by which contaminants get into data on particulate matter can be rainwater. For those intending to harvest accessed at the Air Quality Monitoring rainwater for potable use, the web page of the Texas Commission on microbiological contaminants E. coli, Environmental Quality (TCEQ). (See Cryptosporidium, Giardia lamblia, total References.) coliforms, legionella, fecal coliforms, Chemical compounds and viruses, are probably of greatest Information on chemical constituents concern, and rainwater should be tested can also be found on the TCEQ Air to ensure that none of them are found Quality website. (See References.) (Lye, 2002). County health department and city building code staff should also In agricultural areas, rainwater could be consulted concerning safe, sanitary have a higher concentration of nitrates operations and construction of rainwater due to fertilizer residue in the harvesting systems. atmosphere (Thomas and Grenne, 1993). Pesticide residues from crop dusting in Factors Affecting Water Quality agricultural areas may also be present. pH (acidity/alkalinity) Also, dust derived from calcium-rich As a raindrop falls and comes in contact soils in Central and West Texas can add with the atmosphere, it dissolves 1 mg/l to 2 mg/l of hardness to the water. naturally occurring carbon dioxide to Hard water has a high mineral content, form a weak acid. The resultant pH is usually consisting of calcium and about 5.7, whereas a pH of 7.0 is neutral. magnesium in the form of carbonates. (A slight buffering using 1 tablespoon of In industrial areas, rainwater samples baking soda to 100 gallons of water in can have slightly higher values of the tank will neutralize the acid, if suspended solids concentration and desired. Also, a concrete storage tank turbidity due to the greater amount of will impart a slight alkalinity to the particulate matter in the air (Thomas and water.) While Northeast Texas tends to Grenne, 1993). experience an even lower pH (more acidic) rainwater than in other parts of 22
  • 28.
    Catchment surface the valve on the linking pipe between When rainwater comes in contact with a tanks. catchment surface, it can wash bacteria, molds, algae, fecal matter, other organic Water Treatment matter, and/or dust into storage tanks. The cleanliness of the roof in a rainwater The longer the span of continuous harvesting system most directly affects number of dry days (days without the quality of the captured water. The rainfall), the more catchment debris is cleaner the roof, the less strain is placed washed off the roof by a rainfall event on the treatment equipment. It is (Thomas and Grenne, 1993; Vasudevan, advisable that overhanging branches be 2002). cut away both to avoid tree litter and to deny access to the roof by rodents and Tanks lizards. The more filtering of rainwater prior to the storage tanks, the less sedimentation For potable systems, a plain galvanized and introduction of organic matter will roof or a metal roof with epoxy or latex occur within the tanks. Gutter screens, paint is recommended. Composite or first-flush diverters, roof washers, and asphalt shingles are not advisable, as other types of pre-tank filters are toxic components can be leached out by discussed in Chapter 2. Sedimentation rainwater. See Chapter 2 for more reduces the capacity of tanks, and the information on roofing material. breakdown of plant and animal matter To improve water quality, several may affect the color and taste of water, treatment methods are discussed. It is the in addition to providing nutrients for responsibility of the individual installer microorganisms. or homeowner to weigh the advantages Most storage tanks are equipped with and disadvantages of each method for manholes to allow access for cleaning. appropriateness for the individual Sediment and sludge can be pumped out situation. A synopsis of treatment or siphoned out using hose with an techniques is shown in Table 3-1. A inverted funnel at one end without discussion of the equipment is included draining the tank annually. in Chapter 2. Multiple linked tanks allow one tank to be taken off line for cleaning by closing 23
  • 29.
    Table 3-1. TreatmentTechniques METHOD LOCATION RESULT Treatment Screening Leaf screens and strainers gutters and downspouts prevent leaves and other debris from entering tank Settling Sedimentation within tank settles out particulate matter Activated charcoal before tap removes chlorine* Filtering Roof washer before tank eliminates suspended material In-line/multi-cartridge after pump sieves sediment Activated charcoal after sediment filter removes chlorine, improves taste Slow sand separate tank traps particulate matter Microbiological treatment /Disinfection Boiling/distilling before use kills microorganisms Chemical treatments within tank or at pump (Chlorine or Iodine) (liquid, tablet, or granular) kills microorganisms before activated charcoal filter Ultraviolet light after activated charcoal kills microorganisms filter, before tap Ozonation after activated charcoal kills microorganisms filter, before tap Nanofiltration before use; polymer membrane removes molecules -3 -6 (pores 10 to 10 inch ) Reverse osmosis before use: polymer removes ions (contaminants membrane (pores 10-9 inch) and microorganisms) *Should be used if chlorine has been used as a disinfectant. Adapted from Texas Guide to Rainwater Harvesting, Second Edition, Texas Water Development Board, 1997. 24
  • 30.
    In either case,it is a good idea to Chlorination carefully dilute the chlorine source in a Chlorination is mentioned here more for bucket of water, and then stir with a its historical value than for practical clean paddle to hasten mixing application. Chlorine has been used to (Macomber, 2001). Chlorine contact disinfect public drinking water since times are show in Table 3-2. 1908, and it is still used extensively by rainwater harvesters in Hawaii, the U.S. The use of chlorine for disinfection Virgin Islands, and in older rainwater presents a few drawbacks. Chlorine harvesting systems in Kentucky and combines with decaying organic matter Ohio. Chlorine must be present in a in water to form trihalomethanes. This concentration of 1 ppm to achieve disinfection by-product has been found disinfection. Liquid chlorine, in the form to cause cancer in laboratory rats. Also, of laundry bleach, usually has 6 percent some users may find the taste and smell available sodium hypochlorite. For of chlorine objectionable. To address disinfection purposes, 2 fluid ounces this concern, an activated carbon filter (¼ cup) must be added per 1,000 gallons may be used to help remove chlorine. of rainwater. Household bleach products, Chlorine does not kill Giardia or however, are not labeled for use in water Cryptosporidium, which are cysts treatment by the Food and Drug protected by their outer shells. Persons Administration. A purer form of with weakened or compromised immune chlorine, which comes in solid form for systems are particularly susceptible to swimming pool disinfection, is calcium these maladies. To filter out Giardia and hypochlorite, usually with 75 percent Cryptosporidum cysts, an absolute 1- available chlorine. At that strength, 0.85 micron filter, certified by the NSF, is ounces by weight in 1,000 gallons of needed (Macomber, 2001). water would result in a level of 1 ppm. Table 3-2. Contact Time with Chlorine Water Water temperature pH 50 F or 45 F 40 F or warmer colder Contact time in minutes 6.0 3 4 5 6.5 4 5 6 7.0 8 10 12 7.5 12 15 18 8.0 16 20 24 UV Light UV light has been used in Europe for common practice in U.S. utilities. disinfection of water since the early Bacteria, virus, and cysts are killed by 1900s, and its use has now become exposure to UV light. The water must go 25
  • 31.
    through sediment filtrationbefore the (See References.) The testing fee is ultraviolet light treatment because usually between $15 and $25. pathogens can be shadowed from the UV Homeowners should contact the health light by suspended particles in the water. department prior to sample collection to In water with very high bacterial counts, procure a collection kit and to learn the some bacteria will be shielded by the proper methods for a grab sample or a bodies of other bacteria cells. faucet sample. UV lights are benign: they disinfect Texas Department of State Health without leaving behind any disinfection Services will test for fecal coliforms for by-products. They use minimal power a fee of $20 per sample. (See for operation. One should follow References.) A collection kit can be manufacturer’s recommendations for ordered from TDSHS at (512) 458-7598. replacement of bulbs. Commercial laboratories are listed in Testing telephone Yellow Pages under Harvested rainwater should be tested Laboratories–Analytical & Testing. For before drinking and periodically a fee, the lab will test water for thereafter. Harvested rainwater should pathogens. For an additional fee, labs be tested both before and after treatment will test for other contaminants, such as to ensure treatment is working. It is metals and pesticides. advisable to test water quarterly at a minimum, if used for drinking. References Harvested rainwater can be tested by a Lye D. 2002. Health risks associated commercial analytical laboratory, the with consumption of untreated water county health departments of many from household roof catchment Texas counties, or the Texas Department systems. Journal of the American of Health. Water Resources Association Before capturing rainwater samples for 38(5):1301-1306. testing, contact the testing entity first to Macomber P. 2001. Guidelines on become informed of requirements for rainwater catchment systems for container type and cleanliness, sample Hawaii. Manoa (HI): College of volume, number of samples needed, and Tropical Agriculture and Human time constraints for return of the sample. Resources, University of Hawaii at For instance, for total coliform testing, Manoa. 51 p. water must usually be captured in a Texas Commission on Environmental sterile container issued by the testing Quality, Air Quality Monitoring, entity and returned within a maximum of www.tceq.state.tx.us/nav/data/pm25. 30 to 36 hours. Testing for pH, html performed by commercial analytical laboratories must be done on site; other Texas Commission on Environmental tests are less time-critical. Quality, chemical constituents, www.tnrcc.state.tx.us/airquality.html A list of county health departments that will test for total and fecal coliform can Texas Department of State Health be found on the Texas Department of Services, county health departments, State Health Services (TDSHS) website. 26
  • 32.
    www.dshs.state.tx.us/regions/default. United States Environmental Protection shtm Agency, drinking water requirements, www.epa.gov/safewater/mcl.html Texas Department of State Health Services, testing for fecal coliforms, Vasudevan L. 2002. A study of www.dshs.state.tx.us/lab/default.shtm biological contaminants in rainwater collected from rooftops in Bryan and Thomas PR, Grenne GR. 1993. College Station, Texas [masters Rainwater quality from different roof thesis]. College Station (TX): Texas catchments. Water Science A&M University. 90 p. Technology (28):290-99. 27
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  • 34.
    Chapter 4 Water Balance and System Sizing The basic rule for sizing any rainwater sufficient. On the other hand, if harvesting system is that the volume of rainwater is intended to be the sole water that can be captured and stored source of water for all indoor and (the supply) must equal or exceed the outdoor domestic end uses, a more volume of water used (the demand). precise reckoning is necessary to ensure adequate supply. The variables of rainfall and water demand determine the relationship How Much Water Can Be between required catchment area and Captured? storage capacity. In some cases, it may be necessary to increase catchment In theory, approximately 0.62 gallons surface area by addition of a rain barn or per square foot of collection surface per outbuilding to capture enough rainwater inch of rainfall can be collected. In to meet demand. Cistern capacity must practice, however, some rainwater is lost be sufficient to store enough water to see to first flush, evaporation, splash-out or the system and its users through the overshoot from the gutters in hard rains, longest expected interval without rain. and possibly leaks. Rough collection surfaces are less efficient at conveying The following sections describe ways to water, as water captured in pore spaces determine the amount of rainfall, the tends to be lost to evaporation. estimated demand, and how much storage capacity is needed to provide an Also impacting achievable efficiency is adequate water supply. the inability of the system to capture all water during intense rainfall events. For Intended End Use instance, if the flow-through capacity of The first decision in rainwater harvesting a filter-type roof washer is exceeded, system design is the intended use of the spillage may occur. Additionally, after water. If rainwater is to be used only for storage tanks are full, rainwater can be irrigation, a rough estimate of demand, lost as overflow. supply, and storage capacity may be Figure 4-1. Catchment areas of three different roofs 29
  • 35.
    Figure 4-2. Averageannual precipitation in Texas, in inches For planning purposes, therefore, these volume of storage capacity that can be inherent inefficiencies of the system installed. need to be factored into the water supply calculation. Most installers assume an Collection Surface efficiency of 75 percent to 90 percent. The collection surface is the “footprint” of the roof (Figure 4-1). In other words, In most Texas locations, rainfall occurs regardless of the pitch of the roof, the seasonally, requiring a storage capacity effective collection surface is the area sufficient to store water collected during covered by collection surface (length rainy times to last through the dry spells. times width of the roof from eave to In West Texas, total annual rainfall eave and front to rear). Obviously if only might not be sufficient to allow a one side of the structure is guttered, only residence with a moderate-sized the area drained by the gutters is used in collection surface to capture sufficient the calculation. water for all domestic use. Some residences might be constrained by the Rainfall Distribution area of the collection surfaces or the In Texas, average annual rainfall decreases roughly 1 inch every 15 miles, 30
  • 36.
    the total availablevolume of such an event is rarely captured. Another consideration is that most rainfall occurs seasonally; annual rainfall is not evenly distributed throughout the 12 months of the year. The monthly distribution of rainfall is an important factor to consider for sizing a system. Monthly rainfall data for selected Texas cities is given in Appendix B. Monthly Rainfall Figure 4-3. Maximum number of dry days Two different estimators of monthly (Krishna, 2003) rainfall are commonly used: average rainfall and median rainfall. Average as you go from east to west (Figure 4-2), annual rainfall is calculated by taking the from 56 inches per year in Beaumont to sum of historical rainfall and dividing by less than 8 inches per year in El Paso. As the number of years of recorded data. one moves westward across the state, the This information is available from prevalence and severity of droughts must numerous public sources, including the also be considered. National Climate Data Center website. To ensure a year-round water supply, the (See References.) Median rainfall is the catchment area and storage capacity amount of rainfall that occurs in the must be sized to meet water demand midpoint of all historic rainfall totals for through the longest expected interval any given month. In other words, without rain. For instance, in West historically for the month in question, Texas, the historic longest span of half of the time the rainfall was less than continuous dry days has exceeded three the median and half of the time rainfall months. For reference purposes, a was more than the median. Median contour map of historical maximum values and average rainfall values for number of dry days in Texas is shown in representative Texas cities are provided Figure 4-3 (Krishna, 2003). If the in Appendix B. rainwater harvesting system is intended Median rainfall provides for a more to be the sole water source for a conservative calculation of system sizing household, the designer must size the than average rainfall. The median value system to accommodate the longest for rainfall is usually lower than the anticipated time without rain, or average value since large rainfall events otherwise plan for another water source, tend to drive the average value higher. In such as a well backup or hauled water. other words, the sum of monthly Also, rainfall from high-intensity, short- medians is lower than the annual average duration rainfall events may be lost to due to the fact that the arithmetic overflow from storage tanks or splash- average is skewed by high-intensity out from the gutters. Although these rainfall events. For planning purposes, intense rainfall events are considered median monthly rainfall can be used to part of the cumulative annual rainfall, estimate water availability to a 31
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    reasonable degree ofcertainty (Krishna, The Water Balance Method Using 2001). Monthly Demand and Supply For example, in the sample calculations One method of determining the at the end of this chapter, the average feasibility of a proposed system is the annual rainfall for Dallas is about 35.0 monthly water balance method. This inches, but the sum of the monthly method of calculation is similar to medians is only 29.3 inches. maintaining a monthly checkbook balance. Starting with an assumed Calculating Storage Capacity volume of water already in the tanks, the Once the median or average potential for volume captured each month is added to rainfall capture is known from rainfall the previous balance and the demand is data and catchment area, it will be subtracted. The initial volume of water necessary to calculate storage capacity. in the tanks would be provided by The decision of whether rainwater will hauling or capturing water prior to be used for irrigation, potable and withdrawing water from the system. An domestic use, or both, will dictate water example is presented at the end of this demand, and therefore, capacity. chapter. A simple method of roughly estimating Data and calculations can be entered on storage capacity popular among an electronic spreadsheet to enable the professional installers is to size the user to compare different variables of storage capacity to meet quarterly catchment area and storage. It is demand. The system is sized to meet suggested that homeowners experiment estimated demand for a three-month with different variables of storage period without rain. Annual estimated capacity and, if applicable, catchment demand is divided by four to yield surface to find individual levels of necessary storage capacity using this comfort and affordability for catchment approach. This approach, however, may size and storage capacity. result in a more expensive system due to As mentioned above: higher storage costs. catchment area and rainfall determine If a rainwater harvesting system is to be supply, and the sole water supply, overbuilding demand dictates required storage ensures a safety margin. As with many capacity. things in life, it helps to hope for the best but plan for the worst. Even when A commitment to conserving water with budget constraints may not allow the water-saving fixtures, appliances, user to install as much storage capacity practices indoors, and low-water-use as a sizing method may indicate, it is landscaping outdoors is an essential important to provide for an area where component of any rainwater harvesting additional tanks or cisterns can be system design. Not only is conservation installed at a later date when finances good stewardship of natural resources, it permit. also reduces the costs for storage capacity and related system components. If the amount of rainwater that can be captured – calculated from roof area and rainfall – is adequate or more than 32
  • 38.
    adequate to meetestimated demand, and efficient water use practices both indoors meets the physical constraints of the and outdoors. building design, then storage capacity can be sized to meet estimated demand. Estimating indoor water demand If the monthly amount of water that can Indoor water demand is largely be captured, accounting for dry spells, is unaffected by changes in weather, less than monthly estimated demand, although changes in household then additional catchment area or occupancy rates depending upon seasons supplemental supplies of water (such as and ages of household members, more groundwater from a well) will need to be water use during the hot summer considered. months, and very minor changes in consumption of water due to increases in In drier areas, no matter how large the temperature may be worth factoring in storage capacity, catchment area may some instances. The results of a study of need to be increased with a rain barn or 1,200 single-family homes by the additional roof area to meet demand. American Water Works Association At the end of this chapter, an example of (AWWA) in 1999 found that the average a water balance calculation is shown for water conserving households used the City of Dallas. approximately 49.6 gallons per person per day (American Water Works Estimating Demand Association, 1999). A water-conserving household will use Table 4-1 can be used to calculate indoor between 25 and 50 gallons per person water demand. Many households use per day. (Note that total gallons per less than the average of 49.6 gallons per capita per day figures published for person found in the 1999 report by the municipalities divide all the water AWWA, Residential End Uses of Water. distributed by the population, yielding a The water volumes shown in the table much larger amount per capita than assume a water-conserving household, actual domestic consumption.) with water-conserving fixtures and good Households served previously by a water practices, such as shutting off the water utility can read monthly demand from while brushing teeth or shaving. Overall their meter or water bill to find monthly demand in showers, baths, and faucet demand for purposes of building a new uses is a function of both time of use and rainwater harvesting system. Divide the rate of flow. Many people do not open monthly total by the number of people in the flow rate as high as it could be the house, and the days in the month to finding low or moderate flow rates more get a daily per capita demand number. comfortable. In estimating demand, measuring flow rates and consumption Water conservation is covered later in in the household may be worth the effort this chapter. Households solely to get more accurate estimates. dependent upon rainwater should adopt 33
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    Table 4-1. EstimatingIndoor Daily Domestic Demand A. B. C. D. E. Water Assumptions Adjustments to Number of Household consumption from AWWA assumptions persons in monthly using Residential End- (adjust up or household demand conserving Use Study down according fixtures to actual use) A x (B or C )x D x 30 Toilets (use only appropriate type) ULFT 1.6 gal/flush 6 flushes/ person/day Dual Flush 1 gal/flush 6 flushes/ liquids person/day 1.6 gal/flush solids Baths & showers Showerhead 2.2 gal/min 5 minutes/ person/day Bath 50 gal/bath NA Faucets 2.2 5 minutes/ (personal gal/faucet/min person/day hygiene, cooking, and cleaning of surfaces) Appliances or uses which are measured on a per-use basis (not a per-person basis): Clothes washer 18–25 gal/load 2.6 loads/week Front-loading (horizontal-axis) Dishwasher 8 gal/cycle 0.7 cycles/day Miscellaneous other Total One can use Table 4-1 if the designer patterns. The average values in the prefers to incorporate known or expected second column are offered for behavioral habits into the water demand information, but as with all averages, are estimates. The values in the first column subject to wide variation based upon are to be multiplied by variables actual circumstances. An example is reflecting your own household water use dual flush toilets – multiply three flushes 34
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    per day liquidonly (1 gpf), and add three designed to use 2.2 gallons per minute flushes per day for solids (1.6 gpf), (3x1) at 60 psi, or 2.5 gpm at 80 psi (Table + (3x1.6) = 7.8 gallons multiplied by 3 4-1). Studies have shown that most persons = 23.4 gpd household demand x people feel comfortable at less than 30 days = 702 gallons per month. The full flow rates, so using the new authors recommend verifying any fixtures (which are the only ones sold assumptions against the records of in the United States since 1992) historical use from a municipal water bill should provide you with an efficient if available. and comfortable experience. Indoor water conservation Hot water on demand. These wall- mounted units heat water just prior to Indoor domestic water conservation can use, eliminating the waste of waiting be achieved by a combination of for hot water from the water heater fixtures, appliances, and water- while cold water is allowed to flow conserving practices. The advantage of down the drain. Hot water loop water-conserving appliances is that they systems keep hot water continuously require no change in household routine. circulating to achieve the same goal, Some water-conserving practices need but can use more energy. Another on- user action, such as turning off the water demand unit heats water quickly only while brushing teeth or shaving; washing when activated by a pushbutton, vegetables in a pan rather than under a rather than circulating water through a stream; washing only full loads of loop, saving both water and energy. A laundry and dishes; and keeping a rebate from San Antonio Water pitcher of water in the refrigerator, rather System (SAWS) is available for than waiting for cold water to arrive installation of this type of on-demand from a faucet. circulation system. Water conservation appliances include: Horizontal-axis (front-loading) clothes Ultralow flush toilets (ULFTs). Since washers. Because clothes are tumbled 1993, only ULFTs with 1.6 gallons through a small volume of water in per flush may be sold in the United the bottom of the drum (rather than States. Older toilets should be washed in a full tub of water), this replaced with the more efficient appliance can save up to half the models. Some of the ULFTs require water of a traditional clothes washer. special early closing flappers to It is also as much as 42 percent more maintain their low-flow rates, so care energy efficient. A list of front- should be taken in purchasing the loading, horizontal-axis clothes correct replacement flapper for washers is maintained by the leaking toilets. If purchasing a new Consortium for Energy Efficiency toilet, those that do not use early online. (See References.) Several closure flappers are recommended. municipal utilities in Texas, including Dual-flush toilets (using less volume City of Austin, SAWS, and Bexar for liquid wastes) are also a good Met, offer rebates for the purchase of choice for a water-wise household. these energy- and water-efficient Faucet aerators and efficient appliances. showerheads. These fixtures are 35
  • 41.
    Estimating outdoor waterdemand A recommended general reference for Outdoor water demand peaks in hot, dry water-wise landscaping is Xeriscape: summer. In fact, as much as 60 percent Landscape Water Conservation, of municipal water demand in the publication B-1584, available online. summer is attributable to irrigation. (See References.) Other plant lists and resources are available at the Texas The water demands of a large turfgrass Master Gardeners’ website. (See area almost always preclude the sole use References.) Many municipal water of harvested rainwater for irrigation. utilities, including those in the cites of El Many urban dwellers capture rainwater Paso, Houston, Austin, San Antonio, and for irrigation of vegetable and the Metroplex area have published ornamental gardens. Because it is free of water-wise landscaping information salts and minerals, rainwater promotes tailored to local climate and soil healthy plant growth. In urban areas, conditions rainwater harvesters may reduce their It is recommended that rainwater water bill by substituting harvested harvesting families install landscapes of rainwater for municipal water for garden native and adapted plants, and also irrigation. ascribe to the seven principles of For both the health of landscape plants Xeriscaping. A water-wise landscape and water use-efficiency, the best way to can be quite attractive, while conserving water plants is according to their needs. water and demanding less care than a For most plants adapted to Texas’ garden of non-native or non-adapted climate, water stress is visually evident plants. well before plant death. Signs of water stress include a gray blue tint to leaves, leaf rolling, and in the case of turfgrass, Principles of Water-Wise Landscaping a footprint that does not spring back. Watering infrequently and deeply has 1.Plan and design for water conservation. been shown to promote plant health, waiting until plants need the water helps 2. Create practical turf areas. the water user to be sure that they are 3. Group plants of similar water needs growing a healthy landscape. together. For planning purposes, historical 4. Use soil amendments like compost to evapotranspiration can be used to project allow the soil to retain more water. potential water demands. Evapotranspiration is the term for water 5. Use mulches, especially in high and use by plants, the combination of moderate watering zones, to lessen evaporation from the soil and soil evaporation. transpiration from the plant leaves. An 6. Irrigate efficiently by applying the right estimated value called potential amount of water at the right time. evapotranspiration is available on the Texas Evapotranspiration website, or 7. Maintain the landscape appropriately can be calculated from weather-related by fertilizing, mowing, and pruning. data. (See References.) 36
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    References Krishna H. 2003. An overview of rainwater harvesting systems and American Water Works Association. guidelines in the United States. 1999. Residential end uses of water. Proceedings of the First American Denver (CO): American Water Rainwater Harvesting Conference; Works Association Research 2003 Aug 21-23; Austin (TX). Foundation. 310 p. National Climate Data Center, Consortium for Energy Efficiency, list of www.ncdc.noaa.gov clothes washers, www.cee1.org/resid/seha/rwsh/rwsh- Texas Evapotranspiration Network, main.php3 texaset.tamu.edu Krishna H. 2001. Rainwater catchment Texas Master Gardeners, systems in Texas. Proceedings of the aggiehorticulture.tamu.edu/mastergd/ 10th International Conference on mg.html Rainwater Catchment Systems of the Xeriscape: Landscape Water International Rainwater Catchments Conservation, publication B-1584, Systems Association; 2001 Sep 10- tcebookstore.org 14; Mannheim, Germany. 37
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    Rainwater Harvesting SystemSizing Sample Water Balance Calculations for Dallas, Texas Two methods of determining system sizing are shown below. In the first example, monthly average rainfall data are used, and in the second example, monthly median rainfall data are used for calculations. Monthly rainfall data for several locations in Texas are provided in Appendix B. Keep in mind that the basic monthly water balance calculation is Water available (gallons) = Initial volume in storage (gallons) + gallons captured – gallons used. In an especially wet month, gallons in storage + gallons captured may exceed storage capacity; storage capacity could become a limiting factor, or a slightly larger cistern may be considered. Assumptions • Demand of 3,000 gallons/month • Collection efficiency of 85 percent • 0.62 gallons per square foot of roof area per inch of rain • 10,000-gallon storage capacity • 1,000 gallons in storage on January 1 to start out. (The water may have been collected between the time of system completion and new home occupancy, or it may be hauled water; systems designed for irrigation use only should be completed in the fall to collect rainwater during the slow-/non-growth season.) • Irrigation volume is estimated based upon a small ornamental landscape, and limited supplemental irrigation, since this example is used for potable supply. Calculations using Monthly Average Rainfall Data First calculate the number of gallons collected in January. Using the average value of 1.91 inches of rain for January in Dallas (from Appendix B), the number of gallons of rainwater that can be expected to be stored in January from a 2,500-square-foot roof assuming 85% collection efficiency is determined from the equation: Rainfall (inches) x roof area x 0.62 gal/sq ft /in. rain x collection efficiency In this example: 1.97in. rainfall x 2,500sq. ft. catchment x 0.62 gallons/in. rain/sq. ft. x 0.85 collection efficiency = 2,595 gallons To calculate gallons in storage at the end of each month, add the volume of water already in storage (1,000 gallons in this example) to the gallons collected and subtract the monthly demand. 1,000 + 2,595 – 3,000 = 595 gallons available in storage at the end of January This calculation is repeated for each month. To help you follow Table 4-2, please read below: The value in Column E is added to Column F from preceding row and then A is subtracted. If calculated storage amount is zero or less, use zero for the next month. Rainfall exceeding storage capacity is ignored (water lost). The table shows that a collection surface of 2,500 square feet is adequate to meet expected demand (Column F should be more than zero at all times, if not the collection area needs to be increased or the monthly demand should be reduced). Calculations using Monthly Median Rainfall Data Table 4-3 shows the results of using monthly median rainfall (Column D), and performing the same calculations as before. Using monthly median rainfall data is a more conservative method, and is likely to provide a higher reliability than using average rainfall data for system sizing. Homeowners can easily try different values for collection surface and storage capacity using an electronic spreadsheet, downloadable in Excel format from the Texas Water Development Board www.twdb.state.tx.us/assistance/conservation/alternative_technologies/rainwater_harvesting/rain. asp 38
  • 44.
    Table 4-2. SampleWater Balance Calculations for Dallas, Texas (Using Average Rainfall and a 2,500-square-foot collection surface) A. B. C. D. E. F. Water Irrigation Total Average Rainfall End-of- demand demand demand rainfall collected month (watering by (gallons) (inches) (gallons) storage hose or (1,000 gal. Month bucket) to start) January 3,000 0 3,000 1.97 2,596 595 February 3,000 0 3,000 2.40 3,162 757 March 3,000 150 3,150 2.91 3,834 1,441 April 3,000 150 3,150 3.81 5,020 3,311 May 3,000 150 3,150 5.01 6,601 6,762 June 3,000 150 3,150 3.12 4,111 7,723 July 3,000 150 3,150 2.04 2,688 7,261 August 3,000 150 3,150 2.07 2,727 6,838 September 3,000 150 3,150 2.67 3,518 7,206 October 3,000 150 3,150 3.76 4,954 9,010 November 3,000 0 3,000 2.70 3,557 9,567 December 3,000 0 3,000 2.64 3,478 10,000* * Note that there were 44 gallons of overflow in December in this example. A 10,000-gallon cistern appears to be appropriate under the given assumptions. Table 4-3. Sample Water Balance Calculations for Dallas, Texas (Using Median Rainfall and a 2,500-square-foot collection surface) A. B. C. D. E. F. Water Irrigation Total Median Rainfall End-of- demand demand demand rainfall collected month (watering by (gallons) storage hose or (1,000 gal. Month bucket) to start) January 3,000 0 3,000 1.80 2,372 372 February 3,000 0 3,000 2.11 2,780 151 March 3,000 150 3,150 2.36 3,109 111 April 3,000 150 3,150 2.98 3,926 887 May 3,000 150 3,150 4.27 5,626 3,363 June 3,000 150 3,150 2.85 3,755 3,968 July 3,000 150 3,150 1.60 2,108 2,926 August 3,000 150 3,150 1.74 2,292 2,068 September 3,000 150 3,150 2.50 3,294 2,212 October 3,000 150 3,150 2.94 3,873 2,935 November 3,000 0 3,000 2.00 2,635 2,570 December 3,000 0 3,000 2.10 2,767 2,337 This table shows that it is critical to start with an initial storage (1,000 gallons), otherwise the cistern may run out of water in February/March, under the given assumptions. 39
  • 46.
    Chapter 5 Rainwater Harvesting Guidelines No national standards exist for rainwater Association (ARCSA) is in the process harvesting systems. As a result, efforts of publishing guidelines for potable and abound to give assistance to those nonpotable rainwater harvesting considering using rainwater as a water systems. The guidelines will be available supply at state and local levels. In Texas on the ARCSA website at www.arcsa- the voluntary approach has been the usa.org. hallmark of water conservation efforts, and a Water Conservation Best Other Voluntary Guidelines Management Practices (BMP) Guide A number of University-level programs produced by the Texas Water have published guidelines that are Development Board (TWDB) in 2004 helpful to rainwater designers and included a section on Rainwater planners. Included among them are Harvesting and Condensate Reuse for Texas Cooperative Extension’s use by water providers. (See guidelines and the University of References.) Guidance in other parts of Arizona’s “Harvesting Rainwater for the country ranges from voluntary Landscape Use,” both of which focus on guidelines such as BMPs to codes and capturing rainwater for outdoor ordinances stipulating minimum irrigation. The University of Hawaii standards for various aspects of College of Tropical Agriculture and rainwater harvesting. The wide variety in Human Resources in Hawaii produced approaches is summarized in this chapter “Guidelines on Rainwater Catchment by sharing a few key examples of the Systems in Hawaii,” which has initiatives that are available to assist the information for people using rainwater planner of a rainwater harvesting system. for potable consumption. (See References.) RWH Best Management Practices These guidelines for potable systems Water Conservation Implementation recommend that storage tanks be Task Force Guidelines. In 2003 a constructed of non-toxic material such as statewide Water Conservation steel, fiberglass, redwood, or concrete. Implementation Task Force was Liners used in storage tanks should be appointed by the TWDB under a smooth and of food-grade material legislative mandate to develop approved by the U.S. Food and Drug recommendations for water conservation Administration (Macomber, 2001). for the state of Texas. Best management practices reached by a consensus of the Building Codes Task Force address rainwater harvesting In addition to voluntary effort, some and air conditioner condensate in the states and municipalities are choosing to Task Force Water Conservation Best establish rules. Ohio, Kentucky, Hawaii, Management Practices Guide (TWDB, Arizona, New Mexico, Washington, 2004). West Virginia, Texas, and the U.S. American Rainwater Catchment Virgin Islands are considering or have Systems Association. The American developed rules related to rainwater Rainwater Catchment Systems harvesting. 41
  • 47.
    Rules, ordinances, buildingcodes, and building expansion must have a homeowner association covenants provision for a self-sustaining water nationwide run the gamut from requiring supply system, either a well or a rainwater harvesting systems on new rainwater collection area and cistern. construction to prohibiting tanks as an The rules for private water systems in eyesore. the U.S. Virgin Islands state that new In Texas, HB 645, passed by the 78th cisterns must have a minimum capacity Legislature in 2003, prevents of 2,500 gallons per dwelling (Virgin homeowners associations from Islands Code, Title 29, Public Planning implementing new covenants banning and Development). outdoor water-conserving measures such The U.S. Virgin Islands specifies that as composting, water-efficient cisterns for hotels or multi-family landscapes, drip irrigation, and rainwater dwellings have a minimum capacity of harvesting installations. The legislation 10 gallons per square foot of roof area allows homeowners associations to for buildings of one story, and 15 gallons require screening or shielding to obscure per square foot of roof area for multi- view of the tanks. story buildings, although the The State of Ohio has the most extensive requirement is waived for buildings with rules on rainwater harvesting in the access to centralized potable water United States, with code on cistern size systems. and material, manhole openings, outlet The City of Portland, Oregon, requires a drains, overflow pipes, fittings, minimum cistern capacity of 1,500 couplings, and even roof washers. gallons capable of being filled with Ohio’s rules also address disinfection of harvested rainwater or municipal water, private water systems. (See References.) with a reduced pressure backflow prevention device and an air gap Cistern Design, Construction, and protecting the municipal supply from Capacity cross-connection (City of Portland, Cistern design is covered by rules in 2000). some states, often embedded in the rules for hauled water storage tanks. In Ohio, Backflow Prevention and Dual- cisterns and stored water storage tanks Use Systems must have a smooth interior surface, and The option of “dual-supply” systems concrete tanks must be constructed in within a residence – potable harvested accordance with ASTM C913, Standard rainwater supplemented with water from Specification for Precast Concrete a public water system with appropriate Water and Wastewater Structures. backflow prevention – is an option that Plastic and fiberglass tank materials and might be explored for residences which all joints, connections, and sealant must cannot collect enough rainwater. meet NSF/ANSI Standard 61, Drinking Water System Components. In most Texas locations, rainfall occurs seasonally, requiring a large storage In the U.S. Virgin Islands, Bermuda, and capacity to hold enough water collected other Caribbean islands (islands without during rain events to last through the dry large reservoirs or adequate groundwater spells. reserves), all new construction and even 42
  • 48.
    Allowing for aconnection to the public For instance, Santa Fe County, New water supply system could serve to Mexico, passed the precedent-setting promote harvested rainwater as a regulation requiring rainwater harvesting supplemental water source to customers systems on new residential or already connected to the public water commercial structures of 2,500 square supply infrastructure. feet and larger. A bill requiring rainwater harvesting systems on all new This “conjunctive” use would require an construction narrowly missed passage in appropriate backflow prevention device the New Mexico legislature (Darilek, to keep rainwater from entering the 2004; Vitale, 2004) public water supply due to a drop in pressure in the utility’s distribution The City of Tucson, Arizona, has system. instituted requirements for water harvesting in its land use code as a The City of Portland has approved means of providing supplemental water supplemental use of public utility water for on-site irrigation. In fact, “storm at a residence since 1996. The code water and runoff harvesting to includes specific guidance for design supplement drip irrigation are required and installation of the system. It also elements of the irrigation system for limits rainwater to nonpotable uses. The both new plantings and preserved Portland Office of Planning and vegetation” (City of Tucson Code, Development publishes a RWH Code Chapter 23). Guide which includes FAQ and the relevant code sections (City of Portland, Water harvesting in Tucson is also 2000). intended to help in meeting code requirements for floodplain and erosion The State of Washington Building Codes hazard management (City of Tucson Council in 2002 developed guidelines for installation of rainwater harvesting Code, Chapter 26). systems at commercial facilities. They 2005 Rainwater Harvesting are similar to the City of Portland Legislation guidelines mentioned above, but require a larger cistern size, determined by the The Texas Legislature passed House Bill size of the catchment area, which is (HB) 2430 in May 2005, establishing a limited to roof areas. In 2003, the rainwater harvesting evaluation Washington State Legislature approved a committee to recommend minimum 10 percent reduction in stormwater fees water quality guidelines and standards for any commercial facility that installed for potable and nonpotable indoor uses a rainwater harvesting system in of rainwater. The committee will also compliance with the guidelines recommend treatment methods for (Washington State Legislature, 2003). indoor uses of rainwater, methods by which rainwater harvesting systems Required Rainwater Harvesting could be used in conjunction with Systems existing municipal water systems, and Perhaps the most supportive ordinances ways in which that the state can further are those requiring rainwater harvesting promote rainwater harvesting. The in new construction. committee consists of representatives from the Texas Water Development Board, Texas Commission on 43
  • 49.
    Environmental Quality, Departmentof NSF International, NSF/ANSI Standard State Health Services, and the Texas 61, Drinking Water System Section of the American Water Works Components, Association. The committee will provide www.nsf.org/business/water_distribut its recommendations to the Legislature ion/standards.asp?program=WaterDis by December 2006. tributionSys Ohio Department of Health Final Rules, References 3701-28-09 Continuous Disinfection, www.odh.ohio.gov/Rules/Final/Chap ASTM. 2004. ASTM C913-98 standard 28/Fr28_lst.htm specification for precast concrete water and wastewater structures. In: Texas Cooperative Extension. 2004. ASTM Book of standards. Rainwater Harvesting. Bryan (TX): Texas Cooperative Extension. City of Portland. 2000. Code guide. Portland (OR): Office of Planning Texas Water Development Board, Water and Development. 18 p. Conservation Best Management Practices Guide, p 96-101, City of Tucson Code, Chapter 23, Land www.twdb.state.tx.us/assistance/cons Use Code, Section 3.7.4.5B. 2004. ervation/TaskForceDocs/WCITFBM City of Tucson Code, Chapter 26, PGuide.pdf Floodplain and Erosion Hazard Vitale L. 2004 Mar 11. [Personal Management, Section 26-10, communication]. Sante Fe County. Detention/retention systems. 2004. Virgin Islands Code, Title 29, Public City of Tucson, Water Harvesting Planning and Development; Chapter Guidance Manual, 5, Building Code; Section 308, Water dot.ci.tucson.az.us/stormwater/educat supply, cisterns, gutters, downspouts, ion/waterharvest.htm wells. 2004. Darilek A. 2004 Mar 11. [Personal Washington State Legislature. 2003 Mar communication]. Office of the New 13. House Bill 2088. Mexico State Engineer. Waterfall P. 1998. Harvesting rainwater Macomber P. 2001. Guidelines on for landscape use. Tucson (AZ): The rainwater catchment systems for University of Arizona College of Hawaii. Manoa (HI): College of Agriculture and Life Sciences. 39 p. Tropical Agriculture and Human Resources, University of Hawaii at Welsh DF, Welch WC, Duble RL. 2001. Manoa. 51 p. Xeriscape…Landscape Water Conservation. Bryan (TX): Texas Cooperative Extension. 16 p. 44
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    Chapter 6 Cost Estimation Developing a budget for a rainwater both potable use and for irrigation. It harvesting system may be as simple as also has a brief section on comparing adding up the prices for each of the costs with other types of water supply. components and deciding what one can The single largest expense is the storage afford. For households without access to tank, and the cost of the tank is based reliable groundwater or surface water, upon the size and the material. Table 6-1 and too remotely located to hook up to shows a range of potential tank materials the existing potable supply and costs per gallon of storage. The size infrastructure, the information in this of storage needed (see Chapter 4, Water chapter will assist in determining how Balance and System Sizing) and the large a system can be installed for a set intended end use of the water will dictate budget, and the range of costs for an which of the materials are most ideal system. For some, the opportunity appropriate. Costs range from a low of to provide for all or a portion of their about $0.50 per gallon for large water needs with rainwater is an exercise fiberglass tanks to up to $4.00 per gallon in comparing the costs with other for welded steel tanks. options to determine which is most cost- effective. This chapter provides some As tank sizes increase, unit costs per information on cost ranges for standard gallon of storage decreases. components of rainwater systems for 45
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    Table 6-1. StorageTank Cost Size Comments Fiberglass $0.50–2.00/gallon 500–20,000 gallons Can last for decades w/out deterioration; easily repaired; can be painted Concrete $0.30–1.25/gallon Usually 10,000 gallons Risks of cracks and leaks or more but these are easily repaired; immobile; smell and taste of water sometimes affected but the tank can be retrofitted with a plastic liner Metal $0.50–1.50/gallon 150–2,500 gallons Lightweight and easily transported; rusting and leaching of zinc can pose a problem but this can be mitigated with a potable- approved liner Polypropylene $0.35–1.00/gallon 300–10,000 gallons Durable and lightweight; black tanks result in warmer water if tank is exposed to sunlight; clear/translucent tanks foster algae growth Wood $2.00/gallon 700–50,000 gallons Esthetically pleasing, sometimes preferable in public areas and residential neighborhoods Polyethylene $0.74–1.67/gallon 300–5,000 gallons Welded Steel $0.80–$4.00/gallon 30,000–1 million gallons Rain Barrel $100 55–100 gallons Avoid barrels that contain toxic materials; add screens for mosquitoes Gutters and downspouts (Table 6-2) are approximately the same cost. For those needed to collect the water and route it desiring professionally installed to the tank. Two types of gutters are materials, costs range from $3.50 to $12 available for the “do-it-yourselfers”: per foot of gutter, including materials vinyl and plastic, which are available for and installation, in 2004. 46
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    Table 6-2. Gutters Cost Comments Vinyl $.30/foot Easy to install and attach to PVC trunk lines Plastic $.30/foot Leaking, warping and breaking are common problems Aluminum $3.50-6.25/foot Must be professionally installed Galvalume $9-12/foot Mixture of aluminum and galvanized steel; must be professionally installed Some method of discarding the first The roof washer, placed just ahead of the flush of rain from the roof is necessary storage tank, usually consists of a tank to remove debris. The simplest method with leaf strainers and a filter. A is a vertical PVC standpipe, which fills commercially available model has a with the first flush of water from the series of baffles and a 30-micron filter. roof, then routes the balance of water to the tank. 47
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    Table 6-3. RoofWashers Cost Maintenance Comments Box Washer $400-800 Clean the filter after Neglecting to clean every substantial rain the filter will result in restricted or blocked water flow and may become a source or contamination Post Filtering w/ Sand $150-500 Occasionally Susceptible to Filter backwash the filter freezing; a larger filter is best Smart-Valve $50 for kit Occasional cleaning Device installed in a Rainwater Diverter diversion pipe to Kit make it self-flushing and prevent debris contamination; resets automatically Roof washers consist of a tank, usually Table 6-4 shows the ranges for pump between 30- and 50-gallon capacity, costs including pressure tanks. Demand- with leaf strainers and a filter. A roof activated pumps such as Grundfos may washer is a critical component of potable not require a pressure tank, and can often systems and is also needed to filter small provide enough water to meet a home’s particles to avoid clogging drip irrigation demand for instantaneous flow. Careful emitters. A wide range of equipment is thought should be given to the available with different flow capacity possibility of multiple simultaneous and maintenance requirements. In Table demands upon the system in determining 6-3 a list of different equipment used to the appropriate size pump. The range for intercept and pre-filter the water shows a pump costs runs from $385 for the low- range of costs from $50 to more than end tankless pump, to more than $1,000 $800. It is important that the rainwater for the combined price of a high-end harvester pick a roof washer that is pump and pressure tank. adequate for the size of collection area. 48
  • 54.
    Table 6-4. Pumpsand Pressure Tanks Cost Comments Grundfos MQ Water Supply $385-600 Does not require a separate System pressure tank Shallow Well Jet Pump or $300-600 These require a separate Multi-Stage Centrifugal Pump pressure tank Pressure Tank $200-500 Galvanized tanks are cheaper than bladder tanks but often become waterlogged, and this will wear out the pump more rapidly For those planning a potable system, or widely depending upon intended end- if a drip irrigation system is used, some use, the desired water quality, and sort of filtration is necessary. Rainwater preferences of the user. As shown in harvesting suppliers can assist the end Table 6-5, combined filtration/ user in purchasing the right equipment disinfection costs can cost up to $1,000 for his/her needs and the expected or more. Chapter 2, Rainwater demand. Harvesting System Components, will assist you in choosing the right filtration It is important for the end user intending and/or disinfection equipment for your to use rainwater for potable supply to include disinfection among the water system. treatment components. The costs vary 49
  • 55.
    Table 6-5. Filtering/Disinfection Cost Maintenance Effectiveness Comments Cartridge Filter $20-60 Filter must be Removes A disinfection changed particles >3 treatment is also regularly microns recommended Reverse Osmosis $400-1500 Change filter Removes A disinfection Filter when clogged particles >0.001 treatment is also (depends on the microns recommended turbidity) UV Light $350-1000; $80 Change UV bulb Disinfects Water must be Disinfection to replace UV every 10,000 filtered water filtered prior to bulb hours or 14 provided there exposure for months; the are <1,000 maximum protective cover coliforms per effectiveness must be cleaned 100 milliliter regularly Ozone $700-2600 Effectiveness Less effective in Requires a pump Disinfection must be high turbidity, to circulate the monitored with can be improved ozone molecules frequent testing with pre-filtering or an in-line monitor ($1,200 or more) Chlorine $1/month manual Monthly dose High turbidity Excessive Disinfection dose or a $600- applied manually requires a higher chlorination may $3000 automatic concentration or be linked to self-dosing prolonged negative health system exposure but this impacts. can be mitigated by pre-filtering recommendations for regular Operating Costs maintenance. But proper operation and There are also operating costs that maintenance of the system does add to should be considered as you prepare total costs. your budget. As with any water treatment system, the cleaner the water Filter cartridges should be replaced per needs to be, the greater the effort manufacturer’s specifications, based required to maintain the system. upon the rate of water use. Fortunately, with filter cartridges, this Some of the operating costs and time just means regular replacement of the expenditures necessary for system cartridges, and with the disinfection maintenance are regularly cleaning system, following the manufacturers’ gutters and roof washers, checking the 50
  • 56.
    system for leaksby monitoring water with no guarantee of hitting a reliable levels, and paying close attention to source of water. The deeper the well, the water use rates to determine if an more expensive the effort will be. Also, invisible leak has sprung. Although the well water can have very high TDS “do-it-yourselfers” can handle all of levels in some aquifers, resulting in these tasks with little added financial “hard” water. Rainwater is naturally soft burden, the time for regular maintenance and has become a preferred option in and operation must be set aside to some parts of rural central Texas with operate a successful system. costs lower than or equal to those of drilling a well, and reliability high Comparing to Other Sources of enough to justify reliance on weather Water patterns, rather than on an aquifer’s In some areas of Texas the cost of water quality and quantity. drilling a well can be as high as $20,000 51
  • 57.
  • 58.
    Chapter 7 Financial and Other Incentives Financial incentives and tax exemptions regulations did not raise a facility’s encourage the installation of rainwater property taxes, by adding Section 11.31 harvesting systems. The Texas to Chapter 11, and Section 26.045 to Legislature has passed bills, and some Chapter 26 of the Texas Tax Code. local taxing entities have adopted rules The Texas Commission on that provide tax exemptions for Environmental Quality (TCEQ) rainwater harvesting systems. A few established procedures and mechanisms public utilities have implemented rebate for use determination under Texas programs and rain barrel distribution Administrative Code (TAC) Title 30, events that encourage rainwater Chapter 17. harvesting by residential, commercial, and industrial customers. In addition to To qualify for the property tax financial incentives, performance exemption, (1) a facility must first contracting provisions in state code can receive a determination from the TCEQ be used to encourage installation of that the property is used for pollution rainwater harvesting systems. This control purposes, and (2) the applicant chapter includes a brief description of then submits this use determination to methods for determining the appropriate the local tax appraisal district to obtain size of an incentive by local the property tax exemption. governments. The Application and Instructions for Use In addition to financial incentives, Determination for Pollution Control administrative contracting rules for state Property and Predetermined Equipment and local governments encourage the use List, as well as instructions for applying of rainwater harvesting as an alternative for Property Tax Exemptions for water source in Texas. Pollution Control Property, are downloadable from the TCEQ website. Tax Exemptions (See References.) Property tax exemption for commercial Property tax exemptions extended (State- installations (State-wide exemption) wide) A constitutional amendment passed as Passed in 2001 by the 77th Texas Proposition 2 by Texas voters in Legislature, Senate Bill 2 amended November 1993 exempted pollution Section 11.32 of the Texas Tax Code to control equipment, including water- allow taxing units of government the conserving equipment at nonresidential option to exempt from taxation all or buildings, from property taxes. part of the assessed value of the property Rainwater harvesting equipment at on which water conservation commercial installations is considered modifications have been made. The water-conserving equipment. The intent taxing entity designates by ordinance or of this amendment to Article VIII of the law the list of eligible water Texas Constitution was to ensure that conservation initiatives, which may capital expenditures undertaken to include rainwater harvesting systems. comply with environmental rules and 53
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    rainwater harvesting equipmentor County property tax exemptions supplies, water recycling and reuse Homeowners planning to install equipment or supplies, or other rainwater harvesting systems should equipment.” check with their respective county appraisal districts for guidance on An application for sales tax exemption is exemption from county property taxes. included as Appendix D, or can be Links to some county appraisal districts, downloaded from the Office of the State as well as the Office of the State Comptroller. (See References.) Comptroller’s Application for Water Conservation Initiatives Property Tax Municipal Incentives Exemption, can be found online. (See In addition to tax exemptions, two Texas References.) cities offer financial incentives in the form of rebates and discounts to their Hays County is one of the fastest- customers who install rainwater growing counties in Texas, and is also harvesting and condensate recovery the county with the most rapidly systems. increasing number of new rainwater harvesting installations in the state. Hays City of Austin Rainwater Harvesting County encourages rainwater harvesting Programs with a $100 rebate on the development The City of Austin Water Conservation application fee. Department promotes both residential and commercial/industrial rainwater For rainwater harvesting systems serving harvesting. (See References.) The City as the sole source of water for a of Austin sells 75-gallon polyethylene residence, Hays County grants a rain barrels to its customers below cost, property tax exemption from county at $60 each, up to four rain barrels per taxes for the value of the rainwater customer. City of Austin customers who harvesting system. Guidelines for purchase their own rain barrels are rainwater harvesting benefits and eligible for a $30 rebate. qualification can be found at the Hays County website. (See References.) Customers may also receive a rebate of up to $500 on the cost of installing a pre- Homeowners in other parts of the state approved rainwater harvesting system. should consider approaching their local The rebate application includes a government to see if such a property tax formula to calculate optimum tank size exemption could be passed in their and a list of area suppliers and locale. installation contractors. (See Sales Tax Exemption (State-wide) References.) Senate Bill 2 exempts rainwater Commercial entities may be eligible for harvesting equipment and supplies from as much as a $40,000 rebate against the sales tax. Senate Bill 2 amended cost of installing new equipment and Subchapter H of the Tax Code by adding processes to save water under the Section 151.355, which states: Commercial Incentive Program. (See “Water-related exemptions. The References.) following are exempted from taxes New commercial or industrial sites that imposed by this chapter: (1) develop capacity to store sufficient water 54
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    on-site for landscapeirrigation may be Best Management Practices Guide (p. able to receive an exemption from 118 to 130), gives an example and the installing an irrigation meter. steps in calculating the net present value of conserved water. San Antonio Water System Large-Scale Retrofit This approach requires the utility to Rainwater harvesting projects are estimate the potential for water savings eligible for up to a 50-percent rebate due to rainwater harvesting systems under San Antonio Water System’s installed and the likely number of (SAWS) Large-Scale Retrofit Rebate participants in a program. Program. (See References.) SAWS will rebate up to 50 percent of the installed Rainwater Harvesting at State cost of new water-saving equipment, Facilities including rainwater harvesting systems, In 2003, the 78th Texas Legislature, to its commercial, industrial, and second session, passed HB9, which institutional customers. Rebates are encourages rainwater harvesting and calculated by multiplying acre-feet of water recycling at state facilities. The water conserved by a set value of bill requires that the Texas Building and $200/acre-foot. Equipment and projects Procurement Commission appoint a task must remain in service for 10 years. The force charged with developing design water savings project is sub-metered, recommendations to encourage and water use data before and after the rainwater harvesting and water recycling retrofit are submitted to SAWS to at state facilities built with appropriated determine if conservation goals are met. money. To qualify for the rebate, an engineering The intent of HB9 is to promote the proposal and the results of a professional conservation of energy and water at state water audit showing expected savings buildings. The bill requires that before a are submitted. state agency may use appropriated The rebate shortens the return on money to make a capital expenditure for investment period, giving an incentive to a state building, the state agency must industry to undertake water-conserving determine whether the expenditure could projects. be financed with money generated by a utility cost-savings contract. Determining How Much of a Financial Incentive a Utility May Wish to Offer If it is determined to be not practicable To determine whether a municipal utility to finance construction with utility cost should consider offering a rebate or savings, rainwater harvesting and water financial incentive to stimulate the use of recycling are encouraged by HB9. rainwater harvesting, benefits and costs In addition the Texas Education Code must be presented on an economic basis. (Section 61.0591) provides an incentive This is most easily accomplished by to institutes of higher education for condensing the factors into terms of achieving goals set by the Texas Higher dollars per acre-foot ($/AF) and Education Coordinating Board (THECB) comparing that to the cost of building a including: new water supply project. The spreadsheet included in the TWDB’s Report No. 362, Water Conservation 55
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    “energy conservation andwater amendments that increase the water- conservation, rainwater harvesting, holding capacity of the soil, and water reuse.” including compost.” The code states that not less than 10 “rainwater harvesting equipment and percent of THECB total base funding equipment to make use of water will be devoted to incentive funding. collected as part of a stormwater system installed for water quality Performance Contracting control.” Another means of encouraging the “equipment needed to capture water installation of water- or energy-efficient from nonconventional, alternate equipment is to pay for the equipment sources, including air-conditioning through the savings in utility bills. This condensate or graywater, for method of financing water conservation nonpotable uses, and metering has been used by commercial and equipment needed to segregate water industrial consumers, and is written into use in order to identify water state code for government buildings in conservation opportunities or verify several locations. water savings.” The Texas Education Code (Chapter Performance contracts serve as a win- 44.901 and Chapter 51.927), the Texas win opportunity for school districts and Local Government Code (Chapter institutes of higher education to effect 302.004), and the State Government improvements on facilities for water- Code (Chapter 2166.406) allow public and energy-conservation without schools, institutes of higher education, incurring net construction costs. state building facilities, and local governments to enter into performance The State Energy Conservation Office, contracts. Performance contracting in Suggested Water Efficiency allows a facility to finance water- and Guidelines for Buildings and Equipment energy-saving retrofits with money at Texas State Facilities, recommends saved by the reduced utility expenditures that use of alterative water sources be made possible by the retrofit. In other explored for landscape irrigation use. words, the water- and energy-conserving (See References.) Suggested water measures pay for themselves within the sources include captured stormwater or contracted period. More information on rainwater, air-conditioner condensate, performance contracting can be found on water from basement sump pump the State Energy Conservation Office discharge, and other sources, in website. (See References.) accordance with local plumbing codes. Following are descriptions of alternative water sources that are eligible for References performance contracts: City of Austin Water Conservation “landscaping measures that reduce Department, watering demands and capture and www.ci.austin.tx.us/watercon/ hold applied water and rainfall, including: (a) landscape contouring, City of Austin Water Conservation including the use of berms, swales, Department, commercial process and terraces; and (b) the use of soil evaluations and rebates, 56
  • 62.
    www.ci.austin.tx.us/watercon/comme www.tnrcc.state.tx.us/exec/chiefeng/p rcial.htm rop2/0611.doc City of Austin Water Conservation Texas county appraisal districts, Department, rainbarrel rebate, www.texascad.com www.ci.austin.tx.us/watercon/rainwat Texas Statutes Tax Code, er.htm www.capitol.state.tx.us/statutes/tx.toc Hays County, rainwater harvesting .htm benefits and qualification, Texas Water Development Board, Water www.co.hays.tx.us/departments/envir Conservation Best Management ohealth/forms.php Practices Guide, p 96-101, Office of the State Comptroller, www.twdb.state.tx.us/assistance/cons application for sales tax exemption, ervation/TaskForceDocs/WCITFBM www.window.state.tx.us/taxinfo/taxf PGuide.pdf orms/01-3392.pdf Office of the State Comptroller, application for water conservation initiatives property tax exemption, www.window.state.tx.us/taxinfo/taxf orms/50-270.pdf San Antonio Water System, large-scale retrofit rebate program, www.saws.org/conservation/commer cial/retrofit.shtml State Energy Conservation Office, www.seco.cpa.state.tx.us/sa_perform contract.htm State Energy Conservation Office, Suggested Water Efficiency Guidelines for Buildings and Equipment at Texas State Facilities, www.seco.cpa.state.tx.us/waterconser vation.pdf Texas Commission on Environmental Quality, application and instructions for use determination for pollution control property and predetermined equipment list, www.tnrcc.state.tx.us/exec/chiefeng/p rop2/guidance.pdf Texas Commission on Environmental Quality, property tax exemptions for pollution control property, 57
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  • 64.
    Appendix A References ASTM. 2004. ASTM C913-98 standard City of Tucson Code. 2004. Chapter 26, specification for precast concrete Floodplain and Erosion Hazard Area water and wastewater structures. In: Regulations, Section 26-10, ASTM Book of standards. Detention/retention systems. American Rainwater Catchment Systems College of Tropical Agriculture and Association. 2003. First American Human Resources. 2000. Rainwater rainwater harvesting conference catchment systems. Manoa (HI): proceedings. Austin (TX). 2003 Aug University of Hawaii at Manoa. 4 p. 21-22. County of Hawaii. Undated. Guidelines American Water Works Association. for owners of rain catchment water 1999. Residential end uses of water. systems. Hilo (HI): County of Denver (CO): American Water Hawaii. 5 p. Works Association Research Darilek A. 2004 Mar 11. [Personal Foundation. 310 p. communication]. Office of the New Banks S, Heinichen R. 2004. Rainwater Mexico State Engineer. collection for the mechanically Darrow K, Saxenian M. 1986. challenged. Dripping Springs (TX): Appropriate technology sourcebook: Tank Town Publishing. 108 p. a guide to practical books for village Campbell S. 1983. Home water supply: and small community technology. how to find, filter, store, and conserve Stanford (CA): Volunteers in Asia. it. Charlotte (VT): Garden Way 800 p. Publishing. 240 p. Frasier G. 1974. Water harvesting City of Albuquerque. 1999. Rainwater symposium proceedings. Phoenix harvesting: supply from the sky. (AZ). 1974 Mar 26-28. Albuquerque (NM): Water Use and Gould J, Nissen-Petersen E. 1999. Conservation Bureau. 32 p. Rainwater catchment systems for City of Albuquerque. 2000. A waterwise domestic rain: design construction guide to rainwater harvesting. and implementation. London: Albuquerque (NM): Water Use and Intermediate Technology Conservation Bureau. 4 p. Publications. 335 p. City of Austin. 1995. Sustainable Kinkade-Levario H. 2004. Forgotten building sourcebook. Austin (TX): rain. City of Austin Environmental and Krishna H. 2001. Rainwater catchment Conservation Services Department. systems in Texas. Proceedings of the 400 p. 10th International Conference on City of Portland. 2000. Code guide. Rainwater Catchment Systems of the Portland (OR): Office of Planning International Rainwater Catchments and Development. 18 p. Systems Association; 2001 Sep 10- 14; Mannheim, Germany. A1
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    Krishna H. 2003.An overview of Radlet J, Radlet P. 2004. Rainwater rainwater harvesting systems and harvesting design and installation guidelines in the United States. workshop. Boerne (TX): Save the Proceedings of the First American Rain. Rainwater Harvesting Conference; Speidel DH, Ruesdisili LC, Agnew AF. 2003 Aug 21-23; Austin (TX). 1987. Perspectives on water uses and Lye D. 1992. Microbiology of rainwater abuses. New York (NY): Oxford cistern systems: a review. Journal of University Press. 400 p. Environmental Science and Health Spence CC. 1980. The rainmakers: A27(8):2123-2166. American pluviculture to World War Lye D. 2002. Health risks associated II. Lincoln (NE): University of with consumption of untreated water Nebraska Press. 181 p. from household roof catchment Steadman P. 1975. Energy, environment systems. Journal of the American and building. New York (NY): Water Resources Association Cambridge University Press. 287 p. 38(5):1301-1306. Steward JC. 1990. Drinking water Macomber P. 2001. Guidelines on hazards: how to know if there are rainwater catchment systems for toxic chemicals in your water and Hawaii. Manoa (HI): College of what to do if there are. Hiram (OH): Tropical Agriculture and Human EnviroGraphics. Resources, University of Hawaii at Manoa. 51 p. Still GT, Thomas TH. 2003. Sizing and optimally locating guttering for Morgan D, Travathan S. 2002. Storm rainwater harvesting. Proceedings of water as a resource: how to harvest the 11th International Conference on and protect a dryland treasure. Santa Rainwater Catchment Systems; 2003 Fe (NM): City of Santa Fe. 24 p. Aug 25-29; Mexico City (MX). National Academy of Sciences. 1974. Thomas PR, Grenne GR. 1993. More water for arid lands. Rainwater quality from different roof Washington (DC): National Academy catchments. Water Science of Sciences. 149 p. Technology (28):290-99. National Park Service. 1993. Guiding Texas Cooperative Extension. 2004. principles of sustainable Rainwater Harvesting. Bryan (TX): development. Denver (CO): Texas Cooperative Extension. Government Printing Office. Texas Water Development Board. 1997. Pacey A, Cullis A. 1986. Rainwater Texas guide to rainwater harvesting. harvesting: the collection of rainwater Austin (TX): Texas Water and runoff in rural areas. London Development Board. 58 p. (UK): Intermediate Technology Productions. 216 p. Texas Water Development Board. 2002. Water for Texas – 2002. Austin (TX): Phillips A. 2003. City of Tucson water Texas Water Development Board. harvesting guidance manual. Tucson 155 p. (AZ): City of Tucson. 36 p. A2
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    Vasudevan L. 2002.A study of www.ci.austin.tx.us/watercon/rainwat biological contaminants in rainwater er.htm collected from rooftops in Bryan and City of Austin Green Builder Program, College Station, Texas [masters www.ci.austin.tx.us/greenbuilder/ thesis]. College Station (TX): Texas A&M University. 180 p. City of Tucson. 2003. Water Harvesting Guidance Manual, Virgin Islands Code. 2004. Title 29, dot.ci.tucson.az.us/stormwater/educat Public Planning and Development; ion/waterharvest.htm Chapter 5, Building Code; Section 308, Water supply, cisterns, gutters, City of Tucson Code. 2004. Chapter 23, downspouts, wells. Land Use Code, Section 3.7.4.5B, Use of Water, Vitale L. 2004 Mar 11. [Personal www.tucsonaz.gov/planning/luc/luc.h communication]. Sante Fe County. tm Waterfall P. 1998. Harvesting rainwater Consortium for Energy Efficiency, list of for landscape use. Tucson (AZ): The clothes washers, University of Arizona College of www.cee1.org/resid/seha/rwsh/rwsh- Agriculture and Life Sciences. 39 p. main.php3 Washington State Legislature. 2003 Mar Green Builders, www.greenbuilder.com 13. House Bill 2088. Hays County, guidelines for rainwater Welsh DF, Welch WC, Duble RL. 2001. harvesting benefits and qualifications, Xeriscape…Landscape Water www.co.hays.tx.us/departments/envir Conservation. Bryan (TX): Texas ohealth/forms.php Cooperative Extension. 16 p. International Rainwater Catchment Systems Association, www.ircsa.org Websites National Climate Data Center, American Rainwater Catchment Systems www.ncdc.noaa.gov Association, www.arcsa-usa.org National Oceanographic and Application for Water Conservation Atmospheric Administration, Initiatives Property Tax Exemption, www.noaa.gov www.window.state.tx.us/taxinfo/taxf NSF International, filter performance, orms/50-170.pdf www.nsf.org/certified/DWTU/ City of Austin Water Conservation NSF International, NSF/ANSI Standard Department, 61, Drinking Water System www.ci.austin.tx.us/watercon/ Components, City of Austin Water Conservation www.nsf.org/business/water_distribut Department, commercial process ion/standards.asp?program=WaterDis evaluations and rebates, tributionSys www.ci.austin.tx.us/watercon/comme Office of Arid Land Studies Desert rcial.htm Research Unit, Casa del Agua, City of Austin Water Conservation www.ag.arizona.edu/OALS/oals/dru/ Department, rainbarrel rebate, casadelagua.html A3
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    Office of theState Comptroller, for use determination for pollution application for sales tax exemption, control property and predetermined www.window.state.tx.us/taxinfo/taxf equipment list, orms/01-3392.pdf www.tnrcc.state.tx.us/exec/chiefeng/p rop2/guidance.pdf Office of the State Comptroller, application for water conservation Texas Commission on Environmental initiatives property tax exemption, Quality, chemical constituents, www.window.state.tx.us/taxinfo/taxf www.tnrcc.state.tx.us/airquality.html orms/50-270.pdf Texas Commission on Environmental Ohio Department of Health Final Rules, Quality, property tax exemptions for 3701-28-09 Continuous Disinfection, pollution control property, www.odh.ohio.gov/Rules/Final/Chap www.tnrcc.state.tx.us/exec/chiefeng/p 28/Fr28_lst.htm rop2/0611.doc Organization of American States, Texas county appraisal districts, Rainwater Harvesting from Rooftop www.texascad.com Catchments, Texas Department of State Health www.oas.org/usde/publications/Unit/ Services, county health departments, oea59e/ch10.htm www.dshs.state.tx.us/regions/default. Rain Water Harvesting and Waste Water shtm Systems Pty Ltd., Texas Department of State Health www.rainharvesting.com.au Services, testing for fecal coliforms, San Antonio Water System, large-scale www.dshs.state.tx.us/lab/default.shtm retrofit rebate program, Texas Evapotranspiration, www.saws.org/conservation/commer texaset.tamu.edu cial/retrofit.shtml Texas Legal Directory, county appraisal State Energy Conservation Office, districts, www.texascad.com www.seco.cpa.state.tx.us/sa_perform contract.htm Texas Legislature Online, www.capitol.state.tx.us/ State Energy Conservation Office, Suggested Water Efficiency Texas Master Gardeners, Guidelines for Buildings and aggiehorticulture.tamu.edu/mastergd/ Equipment at Texas State Facilities, mg.html www.seco.cpa.state.tx.us/waterconser Texas Statutes Education Code, vation.pdf www.capitol.state.tx.us/statutes/ed.to Texas Administrative Code, c.htm www.sos.state.tx.us/tac/ Texas Statutes Local Government Code, Texas Commission on Environmental www.capitol.state.tx.us/statutes/lg.toc Quality, Air Quality Monitoring, .htm www.tceq.state.tx.us/nav/data/pm25. Texas Statutes Tax Code, html www.capitol.state.tx.us/statutes/tx.toc Texas Commission on Environmental .htm Quality, application and instructions A4
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    Texas Water DevelopmentBoard, Water www.twdb.state.tx.us/assistance/cons Conservation Best Management ervation/consindex.asp Practices Guide, p 96-101, United States Environmental Protection www.twdb.state.tx.us/assistance/cons Agency, drinking water requirements, ervation/TaskForceDocs/WCITFBM www.epa.gov/safewater/mcl.html PGuide.pdf United States Environmental Protection Texas Water Development Board Agency Safe Drinking Water Act, Conservation, www.epa.gov/safewater/sdwa/sdwa.htm A5
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  • 70.
    Appendix B Rainfall Data The following data are provided for representative Texas cities in various geographical areas to assist in assessing the optimal storage size for a particular rainwater harvesting system. Each rainwater harvesting system designer should assess the variables of water demand, rainfall, catchment surface area, storage capacity, and risk tolerance when designing a rainwater harvesting system, especially one intended to be the sole water source. Abilene Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.03 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 4.35 3.60 5.16 6.80 13.17 9.60 7.52 8.18 11.03 10.68 4.60 6.28 Median 0.81 0.73 0.90 1.88 2.47 2.30 1.69 1.62 2.25 2.09 0.94 0.77 Average 1.00 1.05 1.17 2.05 3.22 2.90 2.03 2.40 2.71 2.56 1.24 1.03 Average annual rainfall 23.36 Amarillo Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.04 0.01 0.10 0.28 0.03 0.00 0.00 0.00 Maximum 2.33 1.83 4.01 5.84 9.81 10.73 7.59 7.55 5.02 6.34 2.26 4.52 Median 0.33 0.42 0.58 0.86 2.45 3.08 2.59 2.79 1.61 0.97 0.43 0.35 Average 0.52 0.55 0.93 1.18 2.67 3.40 2.80 2.93 1.84 1.44 0.59 0.53 Average annual rainfall 19.39 Austin Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.09 0.00 0.00 0.00 Maximum 9.21 6.56 6.03 9.93 9.98 14.96 10.54 8.90 7.44 12.31 7.95 14.16 Median 1.27 2.30 1.73 2.20 3.68 2.89 1.15 1.27 2.98 2.82 1.88 1.42 Average 1.77 2.37 1.90 2.83 4.33 3.54 1.73 2.18 3.17 3.63 2.25 2.26 Average annual rainfall 31.96 Brady Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.10 0.00 0.00 0.06 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 6.40 5.30 4.30 6.02 8.00 7.70 13.55 11.30 9.45 7.04 10.40 7.90 Median 0.60 1.26 0.90 1.78 3.10 1.87 0.85 1.34 2.40 1.70 1.10 0.70 Average 1.03 1.50 1.26 2.07 3.40 2.40 1.80 2.01 2.86 2.34 1.43 1.28 Average annual rainfall 23.38 A7
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    Brownsville Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.07 0.34 0.01 0.00 Maximum 4.79 10.25 5.72 10.35 9.12 8.52 9.43 9.56 20.18 17.12 7.69 3.98 Median 0.77 0.84 0.41 0.84 1.86 2.22 0.96 2.45 4.69 2.92 0.90 0.78 Average 1.31 1.38 0.80 1.62 2.39 2.55 1.50 2.69 5.19 3.62 1.55 1.10 Average annual rainfall 25.70 College Station Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.22 0.1 0.29 0.08 0.23 0.09 0 0 0.32 0 0.19 0.23 Maximum 15.6 9.82 6.07 12.5 11.38 12.63 7.06 10.63 12.13 12.91 8.33 10.72 Median 2.205 2.72 2.12 3.75 4.515 2.895 1.97 1.84 4.12 3.18 2.92 2.635 Average 2.87 2.88 2.5 3.77 4.73 3.79 2.24 2.43 4.3 3.64 3.07 3.15 Average annual rainfall 38.75 Corpus Christi Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.01 0.00 0.00 0.00 0.00 0.03 0.00 0.10 0.49 0.00 0.00 0.01 Maximum 10.78 8.11 4.89 8.04 9.38 13.35 11.92 14.79 20.33 11.88 5.24 9.80 Median 0.99 1.36 0.78 1.39 2.70 2.43 1.04 2.64 4.00 2.60 1.34 0.90 Average 1.54 1.85 1.36 2.03 3.12 3.16 1.80 3.28 5.21 3.50 1.57 1.59 Average annual rainfall 30.00 Dallas Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.25 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.18 0.13 Maximum 8.46 7.60 8.70 15.40 13.74 10.30 7.34 5.12 10.67 14.00 7.54 8.90 Median 1.80 2.11 2.36 2.98 4.27 2.85 1.60 1.74 2.50 2.94 2.00 2.10 Average 1.97 2.40 2.91 3.81 5.01 3.12 2.04 2.07 2.67 3.76 2.70 2.64 Average annual rainfall 35.10 El Paso Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 Maximum 2.23 1.69 2.26 1.42 4.22 3.18 5.53 5.57 6.68 3.12 1.63 3.29 Median 0.29 0.34 0.18 0.09 0.10 0.36 1.18 1.06 0.96 0.55 0.24 0.42 Average 0.42 0.40 0.30 0.21 0.32 0.70 1.57 1.45 1.38 0.71 0.36 0.61 Average annual rainfall 8.43 A8
  • 72.
    Houston Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.36 0.38 0.11 0.43 0.04 0.26 0.45 0.31 0.80 0.05 0.41 0.64 Maximum 9.78 5.99 8.52 10.92 14.39 16.28 8.10 9.42 11.35 16.05 10.07 9.34 Median 2.82 2.63 3.19 2.59 5.02 3.55 2.69 3.52 3.92 3.79 3.27 3.41 Average 3.68 2.95 3.40 3.54 5.36 5.07 3.05 3.69 4.31 4.63 4.09 3.54 Average annual rainfall 48.45 Lubbock Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.00 0.00 0.04 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 4.05 2.51 3.34 5.63 13.38 8.43 7.20 8.85 8.55 10.80 2.67 2.24 Median 0.33 0.39 0.63 1.08 2.23 2.37 2.07 1.78 1.87 0.98 0.45 0.42 Average 0.52 0.62 0.90 1.24 2.64 2.95 2.16 2.15 2.49 1.81 0.67 0.56 Average annual rainfall 18.49 San Angelo Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.01 0.00 0.00 0.26 0.05 0.00 0.00 0.00 0.00 0.00 0.00 Maximum 3.65 4.47 5.00 5.10 11.24 6.01 7.21 8.13 11.00 8.68 3.55 3.98 Median 0.58 0.62 0.65 1.29 2.32 2.09 0.70 1.38 2.38 1.90 0.68 0.33 Average 0.79 1.04 0.92 1.66 2.78 2.20 1.10 1.75 2.83 2.24 0.98 0.76 Average annual rainfall 19.12 San Antonio Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.00 0.01 0.03 0.02 0.00 0.01 0.00 0.00 0.05 0.00 0.00 0.03 Maximum 8.52 6.43 6.12 9.32 12.85 11.95 8.29 11.14 13.09 17.96 8.51 13.96 Median 1.10 1.85 1.27 1.94 3.04 2.70 1.21 2.00 2.24 2.75 1.93 1.09 Average 1.59 1.92 1.66 2.52 3.97 3.61 1.82 2.45 3.08 3.42 2.24 1.69 Average annual rainfall 29.96 Waco Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Minimum 0.03 0.00 0.04 0.12 0.52 0.27 0.00 0.00 0.00 0.00 0.13 0.04 Maximum 5.92 7.69 5.56 13.37 15.00 12.06 8.58 8.91 7.29 10.51 7.03 9.72 Median 1.55 2.00 2.22 2.76 3.87 2.34 0.82 0.96 2.57 2.37 2.29 1.94 Average 1.83 2.28 2.25 3.30 4.49 2.98 1.82 1.76 3.02 3.12 2.40 2.31 Average annual rainfall 31.68 A9
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  • 74.
    Appendix C Case Studies Lady Bird Johnson Wildflower Center Austin 4801 La Crosse Avenue Austin, Texas 78739 (512) 292-4100 http://www.wildflower.org Capacity: 70,000 gallons Catchment area: 17,000 square feet Demand: Gardens and landscaping Harvested rainwater from three separate catchment areas provides 10 to 15 percent of the garden and landscaping irrigation of the Lady Bird Johnson National Wildflower Research Center in Austin. An integral part of its architecture, the Center's rainwater harvesting system serves to not only conserve water, but also as a public education tool. The Center collects water from 17,000 square feet of roof space and can store more than 70,000 gallons in on-site cisterns. One of the most prominent features of the center The entry cistern at the Lady Bird Johnson is the 43-foot native-stone-façade tower cistern, Wildflower Research Center is reminiscent of which is built around a 5,000-gallon storage the stone-and-mortar cisterns used by Hill tank. Metal rooftops totaling an area of 17,000 Country settlers. Water from a 1,200-square- square feet drain into the tower cistern and two foot roof area is conveyed to the entry cistern 25,000-gallon tanks collect a total of about via an aqueduct. 300,000 gallons in an average rainfall year. A pressurized distribution system delivers water from the large tanks to an irrigation system. The municipal water supply is linked to the systems with backflow prevention devices to prevent water contamination. The 3,000-gallon entry cistern, fed by an elevated stone-faced aqueduct draining just less than 1,200 square feet of roof area, is reminiscent of rainwater cisterns used by original Hill Country settlers. The Little House cistern captures rainwater from a roof area of about 700 square feet in the Children’s Area. In addition, the Wetland Pond, the Commons Well, and the Balcony Spring together collect 2,500 gallons per inch of rain from the roofs, although water from these features is not used for irrigation. A11
  • 75.
    H-E-B Austin 6900 Brodie Lane (corner William Cannon Blvd. and Brodie Lane) Austin, Texas 78745 Capacity: 28,000 gallons Catchment area: 50,000 square feet Demand: Native and adapted plant landscape Two 8,000-gallon and two 6,000-gallon painted steel tanks are fed from a 24-inch-diameter collection pipe draining the 50,000-square-foot The H-E-B at the corner of Brodie Lane roof. Using efficient drip irrigation, captured and William Cannon Blvd. in south central Austin irrigates an adjacent rainwater irrigates an adjacent water-thrifty landscape of water-thrifty plants with landscape of native and adapted trees and rainwater stored in four painted steel ornamentals. Walkways and plant labels tanks totaling 28,000 gallons. A 24-inch- enhance the attractiveness of the site. diameter pipe conveys water from the roof to the tanks. The four tanks are connected with 6-inch PVC pipes and valves, allowing a tank to be taken off-line to be drained and cleaned. H-E-B, based in San Antonio, prides itself on environmental stewardship in the communities where its supermarkets conduct business. H-E-B saves 6.2 million gallons of water annually by recycling condensation from manufacturing steam equipment. Tanks are linked with 6- inch PVC pipe. Valves allow taking one or more tank off-line for draining or cleaning. A12
  • 76.
    Sunset Canyon Pottery Dripping Springs 4002 E. Highway 290 Dripping Springs, Texas 78620 (512) 894-0938 Sunset Canyon Pottery supplies all its potable and pottery works water demand with water stored in a 46,000-gallon ferrocement tank. When visiting this site on private property, please first request permission from Sunset Canyon Pottery staff. The ferrocement tank at Sunset Canyon Pottery supplies process water for pottery works, as well as potable water for the straw-bale studio and gift shop. The tank was constructed first by forming an armature of steel reinforcement bars, then spraying on a cement-like material similar to that used for in-ground swimming pools. A13
  • 77.
    New Braunfels MunicipalUtility District New Braunfels New Braunfels Utilities Service Center 355 FM 306 New Braunfels, Texas 78130 The New Braunfels Utilities Service Center, completed in 2004, captures rainwater in four 1,000-gallon plastic-lined galvanized steel tanks, one located at each building wing. Water is used to irrigate the landscape of native and adapted plants. The metal tanks form both a practical and aesthetic feature of the architecture of this public building. Four lined, galvanized steel tanks will capture water for irrigation of native and adapted plants. A14
  • 78.
    Hays County CooperativeExtension Office San Marcos 1253 Civic Center Loop San Marcos, Texas 78666 (512) 393-2120 Capacity: 750-gallon galvanized metal tank 1,600 polyethylene tank Catchment area: 2,500 square feet Demand: Demonstration garden Cost: $1,125 The Hays County Extension Office captures rainwater from half the roof area of its 5,000-square-foot building As a demonstration project, a 750-gallon galvanized in two tanks: a 750-gallon galvanized steel tank captures rainwater from the 5,000-square- foot roof of the Hays County Extension Office. steel tank and a 1,600-gallon black polypropylene tank using existing guttering and downspouts. Plans are in the works for water to be gravity-fed to an adjacent Master Gardener demonstration garden. A15
  • 79.
    Edwards Aquifer Authority San Antonio 1615 N. St. Mary's Street San Antonio, TX 78215 (210) 222-2204 Capacity: 2,500 gallons Catchment area: 1,135 square feet Demand: Landscaping The Edwards Aquifer Authority collects rainwater from a catchment area of 1,135 square feet in two cisterns. Water is delivered through gravity flow into a 500-gallon polypropylene tank in the courtyard area. The second cistern, a 2,000- A 2,000-gallon, ranch-style metal cistern is one of two tanks that capture rainwater for landscaping at the gallon ranch-style metal cistern, is Edwards Aquifer Authority building. (Photo courtesy: located on the front lawn, visible from Lara Stuart) the street. Harvested rainwater is used to irrigate the 266-square-foot courtyard, and 2,700-square-foot lawn. A16
  • 80.
    J.M. Auld LifetimeLearning Center Kerrville 1121 Second Street Kerrville, Texas 72028 (830) 257-2218 Capacity: 6,600 gallons (Two 3,300-gallon stacked concrete ring tanks) Catchment area: 5,000 square feet Demand: Adjacent gardens Pondless waterfall Total Cost: $10,500 Breakdown: Two 3,300 concrete tanks, $4,766 Plumbing supplies, $520 Pump, pressure tank, switch, $1,535 Gutter work, $541 Electrical supplies, $160 Trencher rental, $175 In-kind labor, Kerrville ISD, $2,800 Stacked concrete ring 3,000-gallon tank at the Auld Center, Kerrville, The Auld Lifelong Learning Center of Kerrville showing first flush diverter and Independent School District is a community education cistern. facility operated by Kerrville Independent School District. Installed in 2003, two 3,300-gallon stacked concrete-ring tanks collect rainwater from a 5,000-square-foot roof. Tanks are located at the back corners of the building, with a transverse 3-inch PVC pipe conveying the rainwater drained from the front half of the roof. Five-gallon first flush diverters at each corner capture the dust and debris of the initial runoff of each rainfall event. Tanks are fitted with unique water-level sight gages. Vertical rods the same length as the tank height are suspended on floating platforms within the tank. The length of rod protruding from the tops of tanks indicates water level. Captured rainwater will irrigate several adjacent themed gardens. In addition, a unique water feature, a recirculating waterfall, adds aesthetic interest. A17
  • 81.
    Menard ISD ElementarySchool Menard 200 Gay St. Menard, Texas 76859 Container garden and landscape-plant irrigation Capacity: 1,000-gallon green polyethylene tank Catchment area: 600 square feet Demand: 50 emitters: 20 landscape plants, 30 container garden emitters Total cost: $475 Breakdown: Tank, $400 Connections and valves/roofwasher, $35 Using existing gutters and downspouts, Black poly pipe and emitters, rainwater harvesting techniques were used to $40 create a backyard wildscape. The principles of wildscape construction can be transferred to The rainwater harvesting system serves large wildlife management programs. multiple purposes of education, beauty, and habitat improvement at Menard Independent School District Elementary School. The wildscape provides the requirements of food, water, and shelter for native animals. The demonstration site aids in teaching students about healthful wildlife habitats and container and landscape gardening. The water features, gazebo, and rock walkway enhance the outdoor esthetics of the school. A backyard wildscape at Menard Elementary School demonstrates the requirements of food, water, and shelter for rangeland maintenance conducive to supporting wildlife. Using existing gutters and Menard Elementary School rainwater harvesting installation showing downspout, downspouts from the roof of Menard 1,000-gallon poly tank, and gazebo (left) Elementary School, rainwater is diverted into surrounded by native and adapted landscape two 1,000-gallon green polypropylene tanks. plants. In this very attractive installation, One tank supplies a birdbath made of rocks harvested rainwater (using existing gutter and with natural cavities and a prefabricated pond. downspouts) furnishes water not only to the landscape, but also to a watering pond, Both water features are supplied with water birdbath, and wildlife guzzler. (Photo courtesy: conveyed by gravity pressure through 3/4-inch Billy Kniffen) PVC pipe and drip emitters. Native plants provide a food source and cover for wildlife. A18
  • 82.
    Walker County CooperativeExtension Office Huntsville 102 Tam Road Huntsville, Texas 77320 (936) 435-2426 Capacity: 550-gallon polyethylene tank Catchment area: 1,500 square feet Demand: Master Gardener demonstration plot Total cost: Total: $230 Breakdown: Used 550-gallon tank, $150 Plumbing supplies and fittings, $70 Glue, thinner, and paint, Rainwater captured from the 1,500-square-foot roof $10 of the Walker County Extension office is stored in a 550-gallon polypropylene tank, a type readily The Walker County Master Gardeners and available at ranch supply retailers. The 10-gallon flush diverter is the vertical standpipe visible to the staff of Texas Cooperative Extension, left of the tank. Captured rainwater irrigates an supervised by agricultural county agent adjacent Master Gardener demonstration garden, Reginald Lepley, installed a rainwater foreground. harvesting system at the Walker County Extension office for a cost of less than $250. A used white 550-gallon polypropylene tank was thoroughly cleaned and pressure- washed, and painted with brown latex paint to discourage algae growth. Raising the tank on concrete blocks allows gravity flow to a 10-foot by 25-foot Master Gardener demonstration garden. A detailed parts list, instructions and tips for rainwater harvesting in general, and more information on this installation can be found at urbantaex.tamu.edu/D9/Walker/AG/HomeHort/WCMG/hortdemo/Waterdemo/index A19
  • 83.
    AMD/Spansion FAB25 Austin 5204 E. Ben White Blvd. Austin, Texas 78741 Rainwater drained from the facility’s roofs and groundwater from the building perimeter drains furnish all the water needed for landscape irrigation on AMD’s Spansion site in east Austin. Water is collected and stored in a 10,000-gallon fiberglass tank, and then pressurized through the site irrigation loop using surplus pumps. The water savings has been verified at about 4.75 million gallons per year using online flow meters. In-house engineers designed the system and facilities tradespersons installed the tank, pump, piping, and electricity. The irrigation reclaim system has a three-year return on investment. The plant also has segregated drains that allow the reuse and recycling of rinse water from the wafer manufacturing process for cooling tower and Ultra-pure treatment plant makeup drastically reducing city-supplied water. The water savings from the rinse water reuse system is approximately 210 million gallons per year and had a return on investment of less than one year. A20
  • 84.
    J.J. Pickle ElementarySchool/St. John Community Center Austin Corner of Blessing and Wheatley Avenues Austin, Texas A model of sustainable design and building, the J.J. Pickle Elementary and St. John Community Center in northeast Austin is a joint project of Austin Independent School District and the City of Austin. Water from a portion of the 116,200-square-foot facility drains into three tanks, which provide cooling water to the air-conditioning system. For energy savings, the classrooms, gym, dining area, and City library use sunlight rather than electric lights during the day. The complex opened in January 2002, with operational and maintenance cost savings of $100,000 expected each year. The complex includes a public elementary school, shared gymnasium, a health center, public and school libraries, and a community policing office. The cost of construction is $13.6 million, with the AISD funding about $8.3 million and the Water collected from the roof of the J.J. Pickle City of Austin funding about $5.3 million. Elementary School and St. John Community Center The money came from a 1996 School is stored in three large tanks behind the building and District bond election and a City 1998 used as cooling water for the complex’s air- conditioning system. bond package. A21
  • 85.
    Feather & FurAnimal Hospital Austin 9125 Manchaca Road Austin, Texas 78748 Captured water from the roof, parking lot, and condensate from the air conditioners is the sole source irrigation water for a 1- acre turf landscape at the Feather & Fur Animal Hospital in South Austin. Dr. Howard Blatt first explored ways to make use of an existing hand-dug 18,000-gallon underground cistern. The project has since been expanded to take advantage of other rainwater The Feather & Fur Animal Hospital in South Austin features a standing-seam metal roof for rainwater harvesting. sources. Rainwater collected from a standing-seam metal roof gravity flows into the cistern. Then water from the parking lot flows through a water quality pond with gabion for sedimentation and filtration treatment. From the pond, water flows via a 6-inch pipe to catch basin. A small sump pump empties to a 12,500-gallon fiberglass tank. Additionally, the primary condensation line from the air handlers also drains into the gutter and downspout system, which services the roof. A22
  • 86.
    Pomerening/Dunford Residence Bexar County The Pomerening/Dunford family lives on the western edge of Bexar County and uses rainwater harvesting for all of their potable needs. The four-year-old installation features two 10,000-gallon cisterns that store captured water from a 2,400-square-foot collection area. Two 10,000-gallon cisterns collect rainwater at the Pomerening/Dunford residence in Bexar County. A23
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  • 88.
    Appendix D Tax ExemptionApplication Form A25