Rainwater Harvesting

1. Rainwater Harvesting

2. What is rainwater harvesting- • Capturing the rainwater as it falls on roof-tops, sides of buildings and even concrete pavements • Filter it • Store it in large containers either above ground or underground in sumps for immediate consumption or • Charge the underground using percolation pits for use during dry months • All forms of water found in lakes and rivers start with the rain • Rainwater is naturally pure. Covered storage tank rooftop Outlet tap Cemented or treated earth catchments Ferro cement tank

3. Why harvest rainwater? • Relief of strain on other water supply • Reduce water supply infrastructure costs • Reduced flood flows • Reduced topsoil loss • Improved plant growth • Improve storm water quality • Reduce storm water volume and peak storm water discharges • Improve performance of Water Sensitive Urban Design measures Washing machines WCs Main water supply Gardens A chart showing- how simple rain harvesting system can provide water for toilets, washing machine and garden, letting us save up to half of the mains water we currently use.

4. How it works- Collection of rainwater

5. Technical description- • A rainwater harvesting system consists of three basic elements: a collection area, a conveyance system, and storage facilities. • The collection area in most cases is the roof of a house or a building. A conveyance system usually consists of gutters or pipes that deliver rainwater falling on the rooftop to cisterns or other storage vessels • Both drainpipes and roof surfaces should be constructed of chemically inert materials such as wood, plastic, aluminum, or fiberglass, in order to avoid adverse effects on water quality. • The water ultimately is stored in a storage tank or cistern, which should also be constructed of an inert material. Reinforced concrete, fiberglass, or stainless steel are suitable materials 89mm 140mm 125mm Gutter

6. Storage tanks may be constructed as part of the building, or may be built as a separate unit located some distance away from the building Roof Gutter Downspouts Cover Roof washer (filter) Cistern Tap Typical rainwater catchment's system

7. Storage tank reservoir- Collector device • All rainwater tank designs should include as a minimum requirement: • - A solid secure cover- A coarse inlet filter- An overflow pipe- A manhole, sump, and drain to facilitate cleaning- An extraction system that does not contaminate the water; e.g., a tap or pumpTypes- may be underground or on the ground Cleaning & maintenance door Filter Underground tank

8. Gutter Water collection pipe Tank Water tank on the ground

9. Advantages- • Rainwater harvesting provides a source of water at the point where it is needed. • It provides an essential reserve in times of emergency and/or breakdown of public water supply systems, particularly during natural disasters. • The construction of a rooftop rainwater catchment system is simple • The technology is flexible. • The physical and chemical properties of rainwater may be superior to those of groundwater or surface waters that may have been subjected to pollution, sometimes from unknown sources. • Running costs are low. • Construction, operation, and maintenance are not labor-intensive.

10. Disadvantages- • The success of rainfall harvesting depends upon the frequency and amount of rainfall; therefore, it is not a dependable water source. • Low storage capacities will limit rainwater harvesting so that the system may not be able to provide water in a low rainfall period. Increased storage capacities add to construction and operating costs and may make the technology economically unfeasible. • Cisterns and storage tanks can be unsafe for small children if proper access, protection is not provided. • Rainfall harvesting systems increase construction costs and may have an adverse effect on home ownership. Systems may add 30% to 40% to the cost of a building. • Rainfall harvesting systems may reduce revenues to public utilities.

11. Examples- • CITY- Chennai • AIM- Rooftop rainwater harvesting for immediate consumption • ANNUAL RAINFALL- 51” or 1290mm

12. Working- • Rain water collected on roof • Flows through drain pipe • First flush discard some initial water • Water flows through a filter- bottom to top • Store in a sump • Pump the water to tank • Store in a overhead tank- to a house.

13. Designing a rainwater harvesting system- • Water requirements & usage by a family- • Every person needs around 135 liters of clean water per day • These needs may range from 100 to 200 liters based on geographical locations & life styles. • 135 liters per day includes- drinking, cooking, washing, bathing & gardening.

14. Typical family of 5-annual consumption and cost- • Family of 5 needs 135 liters/person/day will need 2,46,375 liters in a year. • How much water can be harvested in a house- • Considering a typical house plot is about 2,400sq.ft. • If we harvest entire 129cm of annual rainfall, it will yield 700 liters of fresh water/ground/day. • This will result in 2,55,500 per year.

15. How much a RWH unit costs- • Actual cost will depend upon specific RWH design, size of facility, house and percent of rainwater harvested and stored. • SUMP: 12,000 liter sump will cost around Rs.50,000 or about Rs.3.50 per liter for large sumps. • DRAIN PIPES: Rs15 to 30 per running foot • BENDS AND ELBOWS: around rs20 to 75 per piece. • FILTER CHAMBER OF 2’X2’X2’ WITH PEBBLES ANDSAND: Rs1,500 • 10’ DEEP PERCOLATION PIT WITH SAND,PEBBLES,AIR VENT AND A PERFORATED SLAB ON TOP: Rs2,500 • ADD LABOUR COST, SUPERVISION & TRANSPORTATION: 5%