PUNE: Till 2002, the 57 flats of Greenland-2 society in Vimannagar had a huge water problem. Their borewell would dry up, and the dependency on two water tankers per day throughout the year boiled down to about Rs 25,000 a month.

The society then installed a rainwater harvesting system in 2003 by spending Rs 52,000 and the borewell yield increased to nine hours a day from just one. And now, when citizens across Pune are grappling with water shortage, Greenland-2 society residents have not commissioned a single water tanker since December 2009.

Col Shashikant Dalvi (retd), the chairman, had designed and implemented the rooftop rainwater harvesting (RWH) project. "On the completion of the RWH project in 2003, our borewell yield went up to nine hours a day. Now, a single borewell gives us 24-hours of water, and we have not felt the need to call for a water tanker," he said.

For the 175-odd residents of this society, water tanker dependency has been reduced to zero, while water shortage in the rest of the city has not affected them at all. "The system has helped us save water and money. The amount of water a tanker carries is about roughly 12,000 liters. Since we have cut our tanker requirement to zero, we have helped save approximately 24,000 liters per day," said Dalvi.

What works for them can work for many societies in the city. Dalvi works out the mathematics for RWH. "Pune's standard rainfall is 770 mm/year. A 1,000 sq ft rooftop area yields about 70,000 liters of rainwater per year. This means that one acre of rooftop area can yield 25 lakh liters of rain water," said Dalvi adding that there are many societies in Vimannagar who need 20 to 25 tankers per day.

Dalvi said that RWH means channelizing rainwater falling on the rooftop or other catchment areas, through drain pipes and a filtration system into a storage place like an open well, borewell, or underground tanks. "Rainwater flows through pipes fitted with a filter assembly. The flush valve is kept open in the beginning of the monsoon for two to three hours to avoid acid rain. Later, the filter catches the impurities in water passing through it. The water then passes through the underground pipes into the borewell," he said, adding that there are eight such pipes in the society.

Their effort has also raised the local area water table. "The quality of water improves with passage of times. The civic body gives a five per cent incentive to the society for its RWH project," he said.