Thirsty Indian metropolis finds an answer in the rain

Chennai has devised ways to capture and reuse rainwater to help solve its shortage.

By Vijaysree Venkatraman | Contributor to The Christian Science Monitor

from the March 20, 2008 edition

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Chennai, India - Five years ago, the Mylapore temple tank – a man-made pond located at the ancient Kapaleeswarar Temple in the south Indian city of Chennai (formerly Madras) – was little more than a vast, dry bed of cracked clay. Neighborhood boys traipsed down the symmetrical steps to the rectangular reservoir, the famed venue of religious "float" festivals, to play their evening game of cricket.

Today, the replenished tank teems with fish.

Water scarcity plagues this thirsty metropolis, home to 7.6 million people and an international hub for software development and business-processing operations.

Chennai's efforts to tackle its water shortage bears watching. By 2030, about 60 percent of the world's population is expected to be living in similar large metro areas with limited natural resources.

The renovated temple tank with its greenish water offers reassuring evidence that efforts to harvest rainwater here – a pragmatic step to fight water shortage – have begun to yield results.

Geography does not favor Chennai: No major river flows through this semi-arid city. But the city averages 48 inches of annual rainfall, six times more than Phoenix. Historically, importing water from neighboring states has been fraught with political tensions.

Wanting to come up with their own solutions, Chennai residents started digging bore wells deep into the earth, right in their backyards even as the surface water bodies – wells, ponds, and springs – dried up during years of drought.

But when groundwater is the primary water source, the challenge of replenishing the aquifer remains. Otherwise, well water could turn brackish or the well run dry. The water table has a chance of staying healthy if rainwater does not escape into the adjoining sea, but paved roads, concrete pathways, and storm drains make such runoff inevitable.

In September 2003, a government ordinance required Chennai's buildings to capture rainwater.

Rainwater, which collects in driveways and rooftops of buildings, is now channeled through filtration pits and funneled into existing wells and tanks. In certain cases, it is allowed to percolate into the earth to replenish the aquifer via a network of pipes.

At Akash Ganga, a model home run by the Chennai Rain Center, visitors can see several rain-harvesting techniques in use. (The center's symbol is an upturned umbrella.) Director Sekhar Raghavan educates visitors on ways to recharge groundwater.

"Capturing rainwater where it falls is a straightforward option – environmentally sustainable and economically viable," says Prof. S. Janakarajan of the Madras Institute of Developmental Studies in Chennai. Engineering marvels such as desalination plants or huge dams have not given permanent solutions to the water problem, he says, because the real answer is simpler. No significant environmental costs accompany this water recycling technique, he points out.

But despite the city ordinance, the full potential of collecting rainwater is yet to be tapped. "In many households it has been a half-hearted effort, and even less has been done for upkeep," says Vincent D'Souza, editor of the Mylapore Times, an English-language newspaper here.

Over the past three decades, rainfall in the tropics – where nearly two-thirds of the earth's rain falls – has increased by 5 percent, according to a study published last year in the American Meteorological Society's Journal of Climate.

If the trend continues, there will be more rainwater for tropical cities like Chennai to harvest.

But unlike Chennai's buildings, its pot-holed roads don't even have a semblance of being ready for the rains.

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