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Published: May 12, 2012 00:00 IST | Updated: May 12, 2012 05:06 IST May 12, 2012

Time to give back to the borewell

S. VISHWANATH

Almost ubiquitous all over Bangalore, the borewell used to symbolise independence and self-sufficiency in water for many households andapartments. Never mind if the city water supply did not give water on a day, switch on the pump and you had as much water as you needed.

Given that the city utility did not give water for new constructions every house and apartment that was getting newly built drilled a borewell

almost even before the ‘Bhoomi Puja' and the excavation for the foundation. No more is this independence and self-sufficiency true.

The city has now a staggering 370,000 to 500,000 borewells depending on who is doing the guesstimating. Many of them are unfortunatelyalso going dry. Those in the old part of the city like Rajajinagar or Jayanagar were drilled at a time when groundwater was available at an

unbelievable 100 ft. or at best 150 ft. These old borewells from the 80s and 90s are being affected first as the groundwater table declines inthe city centre too.

Going dry faster

Those on the periphery of the city are being drilled to depths of 1,200 ft. sometimes. Staggering and unimaginable depths which need lots of

energy too to lift water from such levels. These newer borewells too are going dry faster simply because of the uncontrolled numbers in the

periphery where the city water lines do not reach and therefore the dependence on groundwater is almost cent per cent.

So what needs to be done about it? At the individual building level every borewell must have a recharge structure. Rainwater from the rooftop

must be filtered and led in to the borewell to recharge it. A slug test , filling in a certain volume of water and measuring how long it takes for

the borewell to absorb the given volume, establishes the acceptability and rate of recharge of borewells. This must be done first before therooftop rainwater recharge system is put in place.

Should be tested

Recent slug tests have indicated a rate of recharge of 9,000 litres per hour in some borewells tested.

This will vary from borewell to borewell however and each should be tested before it is recharged.

While direct recharge of a borewell may have a certain risk in terms of silting up or air locks it should not be such a problem for a dried up

borewell or one which has started to yield less water.

Indirect recharge through a recharge well adjacent to the borewell is one another method that can be followed.

The best, however, seems to be a combination of storage of rainwater into a sump tank and recharge of the excess water directly into the

borewell.

S. VISHWANATH

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