COMPONENTS OF A RAINWATER HARVESTING SYSTEM

A rainwater harvesting system comprises components of various stages - transporting rainwater through pipes or drains, filtration, and storage in tanks for reuse or recharge. The common components of a rainwater harvesting system involved in these stages are illustrated here.
1. 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.

Source: A water harvesting manual for urban areas
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. Gutters can be semi-circular or rectangular and could be made using:
Locally available material such as plain galvanised iron sheet (20 to 22 gauge), folded to required shapes.
Semi-circular gutters of PVC material can be readily prepared by cutting those pipes into two equal semi-circular channels.
Bamboo or betel trunks cut vertically in half.
The size of the gutter should be according to the flow during the highest intensity rain. It is advisable to make them 10 to 15 per cent oversize.
Gutters need to be supported so they do not sag or fall off when loaded with water. The way in which gutters are fixed depends on the construction of the house; it is possible to fix iron or timber brackets into the walls, but for houses having wider eaves, some method of attachment to the rafters is necessary.

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.
The following table gives an idea about the diameter of pipe required for draining out rainwater based on rainfall intensity and roof area:
Sizing of rainwater pipe for roof drainage
Diameter Of pipe (mm)
Average rate of rainfall in mm/h
50 75 100 125 150 200
50 13.4 8.9 6.6 5.3 4.4 3.3
65 24.1 16.0 12.0 9.6 8.0 6.0
75 40.8 27.0 20.4 16.3 13.6 10.2
100 85.4 57.0 42.7 34.2 28.5 21.3
125 - - 80.5 64.3 53.5 40.0
150 - - - - 83.6 62.7
mm/ h - millimeters per hour; m - meters

Source: National Building Code
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 and catchment surface.
Source: A water harvesting manual for urban areas.

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 recharge structure. Charcoal can be added for additional filtration.

Source: A water harvesting manual
for urban areas
(i) 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.

(ii) Sand filters
Sand filters have commonly available sand as filter media. 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.
Source: A water harvesting manual for urban areas
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.

(ii. a) Dewas filters
Most residents in Dewas, Madhya Pradesh, have wells in their houses. Formerly, all that those wells would do was extract groundwater. But then, the district administration of Dewas initiated a groundwater recharge scheme. The rooftop water was collected and allowed to pass through a filter system called the Dewas fillter, designed by Mohan Rao , district collecter of Dewas, and engineers of the rural engineering services. The water thus filtered is put into the service tubewell.
The filter consists of a polyvinyl chloride (PVC) pipe 140 mm in diameter and 1.2m long. There are three chambers. The first purification chamber has pebbles varying between 2-6 mm, the second chamber has slightly larger pebbles, between 6 and 12 mm and the third chamber has the largest - 12-20 mm pebbles. There is a mesh at the outflow side through which clean water flows out after passing through the three chambers. The cost of this filter unit is Rs 600.Posted 6 months ago | Delete comment[Image]Chandrasekhar Thimmavajjala [Image]Estate Officer, Sri Sathya Sai Institute of Higher Medical Sciences, BangaloreSee all Chandrasekhar’s activity »Click on the links below to read the article :

Rain Barrel system for harvesting the rain - Deccan Herald, July 06, 2004
Rainwater harvesting in slums - Deccan Herald, July 20, 2004
Better sanitation paves the path to better future - Deccan Herald, December 14, 2004
Let the sun clean up your water for you in this way - Deccan Herald, February, 08, 2005
Using Open Wells for harvesting Rainwater - Deccan Herald, March 01, 2005
Clean and considerate for workers - Deccan Herald, March 22, 2005
Sustainable poly-houses through rainwater harvesting: Indian and Chinese experience - Deccan Herald, April 5,2005
Recharge bore wells through rainwater harvesting - Deccan Herald, June 28, 2005
... Vishwanath and Chitra coordinate this group. ... Did you know that Mahatma Gandhi's house in Porbander, Gujarat had a version of Rain Water Harvesting ? - Blonnet.com, June 15, 2002
Karnataka: Rainwater harvesting as people's movement, The Hindu - Bangalore, June 14, 2002
Rainwater harvesting in Bangalore
RWH Successful installations
Training - National Workshop - Rainwater Harvesting
Rain barrels catalyse water harvesting, Indiatogether.org, March, 2005
Karnataka inches forward in water harvesting, Indiatogether.org, April, 2005
Centre for Alternative Agricultural Media : People's Planning for Water Sustainability:
HouseCalls Jan-Feb 2003 Issue - The Vishwanath's Earth Architecture
Rainwater harvesting gets a boost, The Hindu, October 13, 2002