Rainwater Harvesting

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.

rooftopCoveredstorage tank

Outlet tap

Ferro cement tank

Cemented or treated earth catchments

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

WCsMain water supply

Gardens

Washing machines

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.

How it works-

Filtration

Storage

Recharge and use

Collection of rainwater

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

Gutter

89mm

125mm

140mm

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

Typical rainwater catchment's system

Gutter

Roof

Downspouts

Cover

Cistern Tap Roof washer (filter)

Storage tank reservoir- 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

Collector device

Filter

Underground tank

Tank

Water collection pipe

Gutter

Water tank on the ground

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.

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.

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

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.

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.

Sr. no Activities lit/person/day

1. Drinking 3

2. Cooking 4

3. Bathing 20

4. Flushing 40

5. Washing clothes 25

6. Washing utensils 20

7. Gardening 23

8. Total 135

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.

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 AND SAND:

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%