Dr Shekhar Raghavan plays rain-god when it comes to rainwater harvesting

We have a simple message: We need to conserve the most precious resource on Earth. Water that comes to us as the life giving rain, that has been celebrated in Indian art and poetry through the centuries and that we have taken so much for granted until now when the spectre of empty pots lining the streets of our towns and dry wells in the villages of the country are a harsh reminder that something needs to be done. Rainwater harvesting has finally become an urgent need, but not many people are yet aware of what it means.

At The Rain Centre, a project managed by the Akash Ganga Trust, an NGO based in Chennai, we try to underline why rainwater harvesting is vital. In India, rain is the ultimate source of all fresh water. All the water we have to use for our personal needs is rainwater, with the exception of desalinated water. People don't realise this. They think that rainwater is different from ground water. This lack of awareness is what we are trying to change since 1975!

Why Is It Important?
So what is rainwater harvesting? Very simply put, it is about collecting water when there is rainfall, for use during the non-monsoon months. Rainwater harvesting replenishes the existing ground water.

During a typical monsoon in Chennai for example, it rains for two months for an average of 300 hours (of rainfall). So, unless you are careful in capturing this rainwater, you will be left with no ground water. The objective of rainwater harvesting is to see that not even one drop of rain water is allowed to enter the sewage or flow onto the streets, but is, instead collected into some groundwater bank.

Today rainwater harvesting is a buzzword in urban centres, whereas 15 years ago it was a relatively unfamiliar term. We are not surprised by this and believe it's due to blames it on widespread urban development, In the past, there were a lot more open spaces in cities, so rainwater harvesting took place naturally.

Today, with the paving of garden areas, a high density of buildings and skyscrapers, paved pedestrian platforms and the absence of household wells, rainwater is prevented from percolating into the ground. This results in a steady depletion of ground water due to indiscriminate digging of deep bore wells which do not get adequately replenished with rainwater.

Is It Expensive?
The rainwater harvesting set-up is a one-time expense and if done properly, could cost you between Rs 3,000 to 5,000 for residents living in independent houses. The cost of rainwater harvesting would increase with the size of the building or house.

How To Do Your Bit
The lack of fresh water is something that affects all of us, whether we are rich or poor. The fact is that all human beings need fresh water for their survival. Nobody has the right to abuse the care and consideration of this vital natural resource and it's up to us as citizens to be responsible and actively interested for something as indispensable as ground and fresh water harvesting, for our collective survival.

How To Harvest Rainwater

The Roof Top Method:
One of the easiest ways to harvest rainwater is through the collection of rooftop water which is of good quality if it falls on clean terrace areas. The rainwater is collected through drainpipes connected to this open terrace surface and is redirected to the closest sump or open well in the compound that would ordinarily receive corporation water or ground water. If you need fresh water for immediate use, keep buckets and large vessels in an open area during the rains.

The Absorption Pit Method:
A percolation or absorption pit is a hand bore made in the soil and is filled with pebbles and river sand on top. The depth of these pits can be anywhere between four and eight meters depending on the nature of the soil. If the soil is clayey, the pit has to be dug to a depth at which a reasonably sandy stratum is reached. The diameter of these pits will be 25 cm (10 inches). A circular collection chamber with a silt arrester is provided on top.

The Absorption Well Method:
These wells are constructed using cement rings available in the market. The diameter of these rings varies from two ft to six ft. The depth to which these wells are dug depends on the nature of the soil and the diameter depends on the number of roof top pipes that are likely to be connected to each one of these wells. These wells are left unfilled and are covered with RCC (Reinforced Cement Concrete) slabs of suitable thickness to facilitate free pedestrian and vehicular movement on the ground. Rainwater from the terrace is diverted to the existing open well using PVC (poly vinyl chloride) pipes through a filter chamber.