Ten mm of rain over the entire city encompassing 1,250 sq. km is the equivalent of receiving 12,500 million litres of water. It is our duty to make full use of it, says water activist S. Vishwanath

The April showers came on March 31 itself. Since rainfall is recorded at 8.30 a.m. every day in terms of the Indian Metrological Department standard practice, this 25 mm rainfall would figure as the All Fools’ Day rain. In the office where the rain gauge is placed, the rain came as a boon. The empty sump grabbed all 2,300 litres of the filtered rainwater. For the next five days there was no tanker coming in. On April 3, Mother Nature delivered another 15 mm of rain and that meant another 1,350 litres of rainwater into the sump.

Consider what was happening. The water level in the KRS reservoir is fast plummeting and so is the water level in the Kabini Reservoir. There is water to last till May-end at the most. It is not raining enough in the catchment to bring substantial water to the dams yet due to the peculiar orographics and weather characteristics even as the city is being hit by thunderstorms.

Ten 10 mm of rain over the entire city encompassing 1,250 sq. km. is the equivalent of 12,500 million litres of water falling on the city. A staggering figure considering the energy required to bring the daily 1,100 million litres from the Cauvery is an 80 MW system running 24 hours. In another fascinating number this is the equivalent of 12,500 million kg of water being lifted to the skies and being then dashed on the ground by the thunder clouds.

At a household level it is possible for almost all to capture the roof rainwater, filter it and lead it into the sumps which almost every household has. It is of course necessary to keep the roof clean which is a matter of good house-keeping. Let us remember that April on an average has four rainy days and receives 80 mm of rain; and May, when the rest of India is reeling due to the heat, has 12 rainy days in Bangalore with an average of 140 mm of rain.

The law on rainwater harvesting is clear. For every square metre of roof area of a building make a 20-litre storage or recharge system. For every square metre of paved area around a building make a 10-litre storage or recharge system. The recharge system should be in the form of a ring well at least three metres deep.

Easy way out

The simplest way to grab rainwater is to connect the rooftop rainwater drain pipe to a HDPE tank. On the top of the tank place a filter so that the rainwater is cleaned and the dust is filtered out. Place the tank on a pedestal and put a tap to it. This will enable rainwater to be drawn easily. If the water is reasonably clean, use a hose-pipe and put one more filter at the end of the hose-pipe and lead it to your well, borewell or sump and fill that up.

There is no better way for each and every citizen of the city to participate in the solution to the water crisis than through rainwater harvesting.

If all the houses in Bangalore can put in place such a system, the water crisis will be virtually over. If not, there will be much breast-beating and agony in the days to come till monsoon 2013 decides to land over our fair city. Prepare or gently perish. That is water wisdom.