What you need to know about groundwater and your borewell.
The borewell drilling rig arrives on site. It is accompanied by a generator van for providing the power needed to drill. Together, the rig and the generator van can cost a huge sum. The monies have been raised by the entrepreneur and now he has to drill at least 40,000 ft. every month to keep the venture profitable. Amidst a lot of sound and dust the drilling begins and in 24 hours it reaches 500 ft. Water is stuck and the rig disappears.
Here are details you need to know about a borewell
Almost two-thirds of India is hard rock terrain. Basalt, granite and gneiss are the rocks which lie underneath. Here groundwater is not present in huge volumes but is limited to cracks and fissures beneath the rocks.
Borewells provide the bulk of India’s water needs. Including all water requirements, this may be close to 60 per cent of agricultural, industrial and domestic water demand.
India has the largest number of borewells in the world with anywhere between 25 million to 30 million of them being sunk. Their exploitation of groundwater, estimated at 250 cubic km, is the highest in the world.
The location of where to drill comes from a geological exploration called Vertical Electrical Sounding (VES). This is the only scientific way to locate a point to drill. All other methods of point identification are unscientific and in effect mumbo jumbo. Using satellite imagery it is possible to broadly identify zones where groundwater can be available. These are called lineaments or great fissure zones within the earth. However, even within these zones, it is not possible to locate an exact point with the assurance that water will be struck.
There are geological formations called ‘dykes’ – islands of rocks – where groundwater is unlikely to be present because these are generally monolithic formations of rocks without any fissures to hold water.
Recharge rates for the hard rocks are generally low. Only about eight to 10 per cent of the total rainfall percolates into the ground for recharge in semi-arid India.
Groundwater once struck should be closely monitored both for quantity and quality. The quality of groundwater if used for potable purpose should be checked at least every six months. It is preferable to put a volumetric meter and record withdrawal quantities from the ground every month. Arrangements must be made to enhance recharge locally and even regionally. Draught i.e. withdrawal of groundwater, should not exceed recharge so as to keep the system sustainable.
Especially in localities and communities, arrangements should be made to drill the least number of borewells, and groundwater should be shared. Competitive private drilling should be avoided; instead, competitive recharge should be encouraged.
Keeping groundwater resources alive and of required quality should involve every citizen of India. Groundwater literacy and knowledge and good behaviour such as not polluting the soil or water should be encouraged. In that lies groundwater wisdom.