Water wisdomJuly 31, 2010
|We have to look at the sky for our source and the soil below our feet for storage, says S. VISHWANATH|
We know the worth of water when the well runs dry
– Benjamin Franklin
There have been prayers to the rain god in parts of Rajasthan. Frogs are getting married and ‘havans’ are being performed. News comes that the KRS dam on the Cauvery is at an abysmal low and at the Kabini reservoirs, water levels are dropping alarmingly. The Thippagondanahalli reservoir on the Arkavathy is all but empty. The Cauvery, the single largest source of water for Bangalore city, is experiencing unprecedented low flows. These are incredibly difficult times for the citizens of Bangalore as well as the institutions concerned with supplying water.
There is however a different story emerging in a few places in Bangalore. Rainwater harvesting has recently been made mandatory, with a requirement of 20 litres of storage or recharge to be created per square metre of roof area. Preceding this mandate, several households had adopted rainwater harvesting to augment their water supply.
Typically these houses have roofs that sloped towards one direction to make it easy to collect the rainwater. It is then filtered and lead into a sump. The overflow of water from the sump, if any, is led into a recharge well made specifically for this purpose. The typical recharge well is 3 ft. in diameter and 20 ft. deep.
In some houses rainwater is led directly into a recharge well or an existing open well. Since Bangalore has been receiving good rains from a 100 square metre roof area nearly 100,000 litres of rainwater becomes available for storage or for recharging the aquifer.
Slowly the local aquifer is filling up and the wells have begun to yield water. A small half H.P. pump can now draw the 500 litres of water required per day and supply it to the household. This water is available 24/7 and is the cheapest available in the city, costing no more than Rs. 3 per 1,000 litres.
Again and again, nature is telling us that we have to work to get water and that there is no free drink. We have to look at the sky for our source and the soil below our feet for storage. Connecting the sky and the soil is the rainwater harvesting system. The well is the source to receive the rain and when the aquifer is full to enable the stored water to be drawn.
In a country so dependent on groundwater and in a city which has more than 100,000 borewells (possibly 400,000), it is imperative to recharge the shallow aquifer and to control demand. Recharge wells and open wells are excellent structures because they can take in between 1,000 and 4,000 litres per hour, compared to a recharge of 10 litres to 30 litres per square metre per day from lakes and tanks. If we protect our wells, dig more recharge wells, use the opportunity provided by rainwater harvesting learnings and ensure that wells are not polluted then we will have gone a long way in supplementing our water requirements. The impact of urban flooding too will have been minimised.
Being waterwise is to do the little things and do them right. It is also to learn from a tradition of water use and also modern science and marry them in such a way that they bring positive benefits.
Starting from the home is a good beginning, covering the city is ideal.