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Cities and water self-reliance

May 25, 2013

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Examining a recharge well – storm water will be infiltrated into the aquifer here
It is the last fortnight of May and the monsoon is eagerly awaited by the people dependent on dams for water. The Krishnarajasagara dam on the Cauvery had to get an infusion of water from the Hemavathi Dam upstream just to keep the water supply to the cities of Mysore and Bangalore going. Being on the banks of the Cauvery did not help Mysore much as it struggles to pump enough water in the pipes.

Ironically it is been pouring on the cities themselves. Bangalore has received more than 150 mm of rain as pre-monsoon showers. The rain accompanied with squalls on Wednesday evening was 40 mm as measured. What does this mean to the city?

Taken as a whole, the 1250 square kilometre of the city of Bangalore has received 187500 million litres of rain. At 1200 million litres per day this is the equivalent of 156 days of its water. These are staggering volumes especially because it has been raining on the city and not in the catchment of the dams. The rain gods are telling us to go and think local.

If every house had made provisions for rainwater harvesting and every tank in the city had been de-silted and linked to the catchment to collect the rainwater runoff, groundwater would have been full and there would be no shortage of water in the city.

Over a 100 square metre of roof area, 150 mm translates to 15,000 litres of water. On a 200 square metre roof area, typical of a 60 x 40 site construction 30,000 litres of rainwater has fallen in the peak months of summer when the rivers and dams are dry.

While the city as a whole may not be going on a war footing to catch the rain many citizens are. In the layout called Rainbow Drive on Sarjapur Road almost every alternate home is digging a recharge well. Typically these wells are 3 feet in diameter and about 25 feet deep. A recharge well can cost Rs 25,000 approximately.

Rainwater from rooftops is filtered and led into the wells. Storm-water flowing from roads and in drains can also be filtered and led into these recharge wells. This way no water is allowed to go waste and all of it goes to make up and recharge the groundwater keeping the bore-wells running.

A reader from Jayanagar 3rd Block, Mr. Chandrashekhar, is a long time resident of Bangalore. He has an old well in his home and has made provisions to direct the rooftop rainwater through a filter to his well.

The well has water for most parts of the year and he saves water for the BWSSB from anywhere between 6 to 8 months in a year. He makes the point that there are many such old open wells in Jayanagar and that all of them can become recharge structures.

People have built special sumps for rainwater and have not had to buy a single tanker of water in these crucial days of shortage.

It is time the good citizens of our cities realized the benefits of local self reliance and looking at the skies above rather than the dams afar for water. Harvesting rainwater in each and every building should be the mantra and the new government should take every step to make this possible as a mass movement.

Coimbatore and the wonderful initiative there called ‘Siruthuli’ is dredging silt from its big tank and making it ready to receive the monsoon. Similarly all tanks in the cities, be it Mysore, Bangalore, Hyderabad or Coimbatore, should be made ready to receive and store as well as recharge as much of the rains as possible.

Big dams alone will no longer be the answer to the growing thirst of our cities. Every effort from all citizens will need to be mobilized. In that lies water wisdom.

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