CHENNAI: The six-acre Mylapore tank, the city’s largest rainwater harvesting structure, now has five borewells on its bed, pumping out water to keep it alive – the state calls it conservation; experts dub it ill-afforded luxury in the time of drought.

The Hindu Religious and Charitable Endowments (HR&CE) department, which is tasked with monitoring temple tanks, revived three borewells and sunk two new ones on the 18th century tank bed last month. Officials are in the process of sinking four more.

Officials said the water will be pumped out to maintain the level at two feet. “We need water for the ducks,” said a senior official, adding that it would also help in conservation. He explained how: “If the ground is dry, the recharge happens slowly. If the tank already has water, it will fill faster.”

This theory doesn’t hold water with experts who say temple tanks are recharged by collecting the excess water from the soil in the same way an open well does at a micro level. “Tanks are both a source and a sink. It helps recharge groundwater by aiding percolation,” said Sekhar Raghavan, director of Rain Centre, adding, “Now is the time they should be desilting tanks for the coming monsoon, not mining water.”

The HR&CE official, however, said the water used was minimal. The pump sets have a capacity of only one horsepower each and the wells are not more than 25ft deep.

To this Raghavan raised concerns saying, “At this juncture, we cannot afford to lose water, which in this case could be due to evaporation.” A survey by Rain Center shows the water table in Mylapore which stood at a depth of 6.2m in May last year has dropped to 7.2m in April this year. The Centre’s observation well, a kilometre from Kapaleeswarar temple, is now dry.

The Mylapore tank is not the only facility to use borewells. When residents are struggling for water, Marundeeswarar temple tank in Thiruvanmiyur has at least three feet of water.

Residents say the water is being extracted from the ground. This is despite a 2009 Madras high court directive to the HR&CE department to seal borewells inside the tank. When TOI contacted an official in charge of the temple, he admitted they sourced water through the borewells “on and off”. “But we pump just enough to keep the fish alive,” he said.

These wells are deeper than those of most residents as the depth of a 20-ft well on the road is less than a 20-ft well sunk into the tank bed, said Madhavi Ganesan, associate professor at the Centre for Water Resources in Anna University who has done a thesis on temple tanks. “Both these temple tanks are at least 10ft-15ft below road level,” said Ganesan, suggesting conduits be set up instead to channelise rainwater into the deep aquifers.

The practice of digging borewells in temple tanks is common in the districts, points out hydrogeologist J Saravanan. “Wells in temple tanks meet the needs of people in times of drought and when the tanks are empty,” he said. But in the city the water in the tanks seems to serve a more aesthetic purpose and keeps at the bay the stark image of a crisis. According to a 2004-report by C P Ramaswami Aiyar Environmental Educational Center, the Chennai Metropolitan Area had 50 temple tanks, of which 22 belong to the 7th century AD, while 10 are from the 17th century.

Temple historian Chitra Madhavan said, all these tanks had inlets that collect water from catchment areas. However, many of these channels have either been lost to encroachment and dumping garbage or been sealed, limiting the tanks to just storing water and not recharging the groundwater.