Bangalore is largely dependent on groundwater. The largest source of water in Bangalore apart from Cauvery water is from borewells.
We are pulling water that has been down there for hundreds of years, that is somebody else’s right as much as it is ours. And the breach of this right can be clearly seen with unequal resource allocation.
How do we get Ground water?
We all live above spaces between soil particles and cracks, fissures and faults in the rocks, which are known as aquifers. Water in these aquifers is rainwater that has trickled down and percolated into the earth. The aquifers are spread independent of property or administrative boundaries. Each time we pull out water from the ground, we are possibly denying someone else of their source of water.
The geology of Bangalore, and most of the Deccan plateau, is hard-rock geology. This type of geological setting is composed of three layers- the top soil where the plants grow, the weathered zone below the top soil and the hard rock. The weathered zone is actually crushed version of the hard rock which holds water in the pores and spaces in between the particles.
When it rains and water percolates down, it passes through the weathered zone and then into the hard rock fissures. A large connected set of fissures, in effect one single body of water under the ground, is called an aquifer. Aquifers in the hard rock are called ‘confined aquifers’ as they are under pressure. Water in the weathered zone is shallow and is referred to as shallow unconfined aquifer and they can travel laterally into the soil. Open wells up to depths of around 80 feet in Bangalore were meant to access water in the shallow unconfined aquifers. Over time these have been dried out, except in certain parts of Bangalore. After open wells started drying, people started digging borewells which were going deeper and picking up water from the fissures in rocks – or from confined aquifers. It is important to note that confined aquifers take more time to recharge the unconfined aquifers.
It’s difficult to predict where you get water in deeper confined aquifers. At depths of 100 to 650 feet, there are a lot of fissures through which water trickles in. There is no way to predict, other than testing each site.
When you dig a borewell and start pulling water out, you are emptying the water in the aquifers which is a finite amount. The process by which water enters into these fissures is called recharge. This can be natural or artificial. Since there is only a finite amount of water underneath, we cannot endlessly keep pumping out water.
As a city, we need to understand how much water is available. This is not an easy task. All the residents in an area need to share where they have dug the bore well, how deep did it go, at what depth did they get water, etc. The data collected across the city can help get a better picture of the city’s aquifers.