Rain Water Harvesting - An Overview
We all know that rain water is one of the purest forms of water
available to us, as it is essentially distilled water.
Hence it is extremely precious, as it does not require any long and
complicated purification process, and is, during the times of rain
fall, readily available, free, and accessible indiscriminately to
With the increases in population the world over, other conventional
water sources are drying up, or are already dry or polluted beyond
So, we are now trying to collect or harvest the pure rain water that
falls for a part of the year, and ensure that it is not wasted.
When the rain water hits the ground (in cities), it runs off down
roads, into drains, mixes with dirt, garbage, etc, - becomes unpotable
- and eventually recahes the seas. It will take another year for this
water to complete the water cycle, and fall back on
the earth as potable rain water - in normal circumstances.
In un-urbanised areas, (that are not concreted over)the rain water
will soak up into the soil and add to the existing water table and
raise the levels of all the local wells and springs, and fill up the
But in cities, we have little space for tanks and large storage of
water, and most natural wells are already dry, because of the
phenomenon of boring, that has sucked out large amounts of water, and
pushed the water table deeper. (Average depth of water table in
suburban Mumbai presently: 200-300 ft)
So there are 2 basic aspects to rain water harvesting:
1) preventing run-off into drains, and replenishing the ground water
2) actual collection and storage of water for a planned future use.
For replenishing the ground water, what is required is that we
channelise the water that falls, and direct it to a particular spot on
the site/plot, (usually the lowest spot, so that the natural slope
assists the water flow) that is not paved over, and from there, the
water soaks up into the ground. A small chamber or dug out is built at
this spot, to aid in this process.
The benefits of this step are long term - as are most efforts and
interventions with the environment.
Collection can be done in many ways - it's as simple as placing a
bucket in the rain. For buildings, there are already roof gutters, and
rain water down-take pipes from the terrace. These need to be
connected to a storage tank, and water can then be collected and
There are several details like understanding how much water to store,
depending on the region that you are in, how to keep the water clean,
how to use it, etc., and for this, there are several resource persons,
web-sites, and Rain Centres (live-examples) that can help you with
Points to note:
Rain water harvesting is not a new phenomenon: the 2000 year old
Kanheri caves in the National Park, have rock-cut water channels that
guide the run-off of the rain water into storage cisterns. As do the
Elephanta Caves, and most examples of rock-cut architecture.
Several traditional settlements and buildings have incorporated rain
water harvesting features into their design. For eg.: houses in Cambay
in Gujarat, all have an underground storage tank, that stores the rain
water run-off, and provides the households with year round supply of
potable water, as well keeps the house cool, in this hot and arid
Hope this answers your question.
Centre for Environmental Research and Education (CERE)
Jaganath Shankar Seth Chowk Municipal School
3rd Floor - Room # 78
Mumbai - 400 007
Tel: (+ 91 - 22) 2381 1581