Rain Water Harvesting

Rainwater Harvesting simply put is the direct collection of rain water. The idea is to catch the rain as it falls over building surfaces and  channel it through pipes to pre-defined storage points.

The rainwater collected is then stored & filtered for immediate use or for recharging the groundwater to be used later though borewells.

Why do we need Rainwater Harvesting?

We get a lot of rain, yet we do not have enough water.

Why?

The answer is simple. Because we still do not use rain water to its fullest value.

We generally receive rainfall in heavy showers followed by dry spells. When it rains heavily the soil is not able to absorb water at the rate of rainfall. As a result most of the rain drains away. Leaving very little for storage & the recharge of groundwater.

This makes most parts of India experience lack of water even for domestic uses.

Thus it does not matter how much rain we get, if we don’t harvest it.

The amount of water that can be harvested depends upon the rainfall in the area, the size of the catchment area & the percentage of rain that can be collected.

Suppose the system has to be designed for a building with a rooftop area of 414 sq. m.

Area of the catchment  = 122.20+291.84= 414.04 sq. M.
Avg Mumbai annual rainfall  = 2400 mm (2.4 m)
Runoff coefficient (% of water that can be potentially harvested) 0.85

Annual water harvesting potential for this building will be

414 x 2.4 x 0.85 i.e. 844.00 cu. m.

This  is 8,44,000 litters approx.