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This week we conclude our series on rainwater harvesting with the 7 different components and stages involved in harvesting rainwater.

Water shedding has already become a reality, and alternative methods to store water will have to be explored. We hope that you have found the series helpful to equip you to make an informative decision on harvesting rainwater.

1. Catchment

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.

2. Coarse mesh at the roof to prevent the passage of debris

3. Gutters

Gutters are channels all around the edge of a sloping roof to collect and transport rainwater to the storage tank. They can be semi-circular or rectangular and could be made using locally available materials. 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.

4. Conduits

Conduits are pipelines 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:

5. 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 – millimetres per hour; m – meters

6. Filter

The filter is used to remove suspended pollutants from rainwater collected. 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.

7. Storage facility

There are various options available for the construction of these tanks with respect to the shape, size and the material of construction.

Source: http://www.rainwaterharvesting.org/urban/components.html

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