Rain water harvesting
- 2. Rainwater Harvesting Rainwater harvesting is the accumulation and deposition of rainwater for reuse before it reaches the aquifer. It is the process of intercepting storm- water runoff and putting it to beneficial use.
- 3. • To arrest groundwater decline and augment ground water table • To beneficiate water quality in aquifers • To conserve surface water runoff during monsoon • To reduce soil erosion • To inculcate a culture of water conservation.
- 4. Rainwater harvesting provides an independent water supply during regional water restrictions and in developed countries is often used to supplement the main supply. It provides water when there is a drought, can help mitigate flooding of low-lying areas, and reduces demand on wells which may enable ground water levels to be sustained. It also helps in the availability of potable water as rainwater is substantially free of salinity and other salts. By harvesting and using rainwater we can: Increase water availability for on-site vegetation Reduce on-site flooding and erosion Reduce water bills and groundwater pumping Extend the life of landscaping (rainwater is usually low in salt content and relatively high in nitrogen)
- 5. 1.PASSIVE RAINWATER COLLECTION: Passive rainwater collection is the act of slowing down rainwater and letting it infiltrate on site rather than channeling it into the storm drain system. A passive system uses earthworks to control surface water flow and uses the soil as the storage container. Intercepted rainwater can be collected, slowed down and retained or routed through the site landscape using microbasins, swales and other water harvesting structures. Redirecting the roof downspout into a landscaped area is an example of pasive rainwater harvesting
- 6. 2. ACTIVE RAINWATER HARVESTING: Active rainwater collection systems integrate a storage container, a tank or cistern, into the system to catch rainwater runoff for later use on the property. These tanks can be installed above or below ground. Above ground systems usually rely on gravity to disperse the water and serve smaller areas. The in ground system requires a pump but can provide water throughout the site.
- 7. COMPARISON: 1. The active systems bring a great advantage : water can be stored and used when the soils are dry (instead of while the ground is soaked from the same rain that filled your tank). 2. Active systems are also more complex than passive systems, cost more and require more maintenance.
- 8. The concentration of contaminants is reduced significantly by diverting the initial flow of runoff water to waste. Improved water quality can also be obtained by using a floating draw-off mechanism and by using a series of tanks, withdraw from the last in series. The stored rainwater may need to be analyzed properly before use in a way appropriate to ensure its safe use The quality of collected rainwater is generally better than that of surface water. Contamination is always possible by airborne dust and mists, bird feces, and other debris, so some treatment may be necessary, depending on how the water will be used. Quality of harvested water
- 9. According to the extent to which water is purified, rainwater can replace domestic functions in a household.
- 10. Rainwater harvesting systems can be installed with minimal skills. The system should be sized to meet the water demand throughout the dry season since it must be big enough to support daily water consumption. Specifically, the rainfall capturing area such as a building roof must be large enough to maintain adequate flow. The water storage tank size should be large enough to contain the captured water System setup.
- 11. Rooftops: If buildings with impervious roofs are already in place, the catchment area is effectively available free of charge and they provide a supply at the point of consumption. Paved and unpaved areas i.e., landscapes, open fields, parks, stormwater drains, roads and pavements and other open areas can be effectively used to harvest the runoff. The main advantage in using ground as collecting surface is that water can be collected from a larger area. This is particularly advantageous in areas of low rainfall.
- 12. Waterbodies: The potential of lakes, tanks and ponds to store rainwater is immense. The harvested rainwater can not only be used to meet water requirements of the city, it also recharges groundwater aquifers. Stormwater drains: Most of the residential colonies have proper network of stormwater drains. If maintained neatly, these offer a simple and cost effective means for harvesting rainwater. From where to harvest rain 32
- 13. 1. Catchments 2. Collection gutters 3. Coarse mesh 4. Rain head inlet filter 5. First flush diverter 6. inlet screen 7. Collection cistern 8. Overflow port 9. Auto fill/ Automatic top up mechanism 10.Pump 11.Water filter 12.Water level indicator
- 14. Catchments: The catchment of a water harvesting system is the surface which directly receives the rainfall and provides water to the system. It can be a paved area like a terrace or courtyard of a building, or an unpaved area like a lawn or open ground. A roof made of reinforced cement concrete (RCC), galvanised iron or corrugated sheets can also be used for water harvesting.
- 15. 2. Coarse mesh at the roof to prevent the passage of debris. 3. Gutters: Channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank 4. Conduits- Conduits are pipelines or drains that carry rainwater from the catchment or rooftop area to the harvesting system. Conduits can be of any material like polyvinyl chloride (PVC) or galvanized iron (GI), materials that are commonly available.
- 16. 5. First-flushing: A first flush device is a valve that ensures that runoff from the first spell of rain is flushed out and does not enter the system. This needs to be done since the first spell of rain carries a relatively larger amount of pollutants from the air.
- 17. 6. Filter The filter is used to remove suspended pollutants from rainwater collected over roof. A filter unit is a chamber filled with filtering media such as fibre, coarse sand and gravel layers to remove debris and dirt from water before it enters the storage tank or recharges structure. a. Charcoal water filter A simple charcoal filter can be made in a drum or an earthen pot. The filter is made of gravel, sand and charcoal, all of which are easily available.
- 18. b. Sand filters are easy and inexpensive to construct. These filters can be employed for treatment of water to effectively remove turbidity (suspended particles like silt and clay), colour and microorganisms. In a simple sand filter that can be constructed domestically, the top layer comprises coarse sand followed by a 5-10 mm layer of gravel followed by another 5-25 cm layer of gravel and boulders.