Chennai is on a list of cities likely to run out of ground water by 2020

The Koda family, who live in Sabari Terrace, an apartment complex located along Chennai's IT corridor, use only rain water for three months a year; there is no piped water supply in this area. When the parched city received its first showers on Saturday, the 56 families who live here collected thirty thousand litres in a little over an hour by harvesting every drop of rain from their 25,000 square foot terrace.

Until last year they let the rain water recharge the groundwater table. Today, the collected water is stored, after treatment, in massive underground tanks with only the surplus released into the ground. This brings about enormous savings in buying water from private tankers.

"When we recharge ground water we have to wait for six months for it to get into our wells to use that water. But on OMR (Old Mahabalipuram Road), where there is no piped water, we need water now. So if it rains today we collect the water and in two hours we get to use. Thirty thousand litres means we save around Rs 5,000," Harsha Koda, who is the prime mover of the project and also Secretary of the residents association, said.

His wife, Prabha Koda, highlights the potential of this method of rainwater harvesting.

"From every square foot of terrace surface area we can take one litre of water if it rains for an hour. It's as simple. We have a 25,000 square foot terrace and we get at least 25,000 litres in an hour. If there's a three-hour downpour we collect one lakh litres, completely filling up our tanks with rain water sufficient for the 56 flats for three days," she explains.

The success that the Kodas of Sabari Terrace have found in this method of rainwater harvesting has persuaded residential communities across the city to replicate the model, in the face of a 40 per cent cut in piped water supply and private water tankers charging double their normal fee.

Residents of Central Park South, another apartment complex not far from Sabari Terrace, have already begun diverting harvested rainwater to one of their underground tanks, something Rakesh Ohri, the Secretary of the association, says is "the need of the hour".

In 2001, former Tamil Nadu Chief Minister J Jayalalithaa made rainwater harvesting mandatory.

According to Rain Centre, a Chennai-based NGO, the order initially led to a six-metre increase in groundwater tables. However, poor implementation over the years led to a recurrence of old problems. Today, with water scarcity hitting hard, many are revisiting methods of rain water harvesting.

As Chennai struggles with unprecedented levels of water scarcity and the city on a list of those likely to run out of ground water by 2020, residents are graduating from harvesting rain water to recharge the water table to using rain water directly.

Many say it is a model worth replicating.