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Pouring rain

May 6, 2008

WATER WISE

How do we preserve rain? S. VISHWANATH

City centres and slightly downwind areas receive 15 per cent more rain than the suburbs

— Photo: G. Moorthy

GET WISER: Being water wise is to understand that rain, the primary source of all water, has to be stored or recharged judiciously While in the countryside rain is a joyful event, in a city it is met with grumbles because it disrupts plans for an evening out or causes floods on the streets or causes power breakdowns. Interestingly, city centres and slightly downwind areas receive up to 15 per cent more rain than the suburbs. It rains more in the city because of the heat island effect — the concrete and asphalt capturing and radiating heat. The intensity of the rainfall also seems to be more in the city.

All the more reason for us to be prepared and to take steps to convert what we perceive to be a nuisance into a resource. The first step is to calculate the rain that falls and the number of rainy days. A rainy day or a wet day is when it rains more than 2.50 mm. This information is available on the India Meteorological Department website and Indiawater.org portal.

The next step is to calculate or find out your plot area and roof area. The next step is to find out the monthly average rainfall. Finally make the choice of filtering rainwater from the rooftop and storing it in a sump. A sump of 6,000 litres is ideal for a 100 square metre roof area but even 2,000 litres of storage will do. Pick the overflow and lead it into a recharge well. Do the same with the plot runoff. A recharge well is typically three ft. in diameter and about 20 ft. deep.

Being water wise is to understand that rain in a city is a blessing to be carefully stored. It does not matter how much it rains, it matters more what we do with the rain.

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