The Calcutta Municipal Corporation (CMC) will soon make rainwater harvesting compulsory for multistoreyed buildings to check the drop in groundwater level.

“There are places in the world where people are suffering because of lack of water resources. If we do not take appropriate steps now, we will soon face similar problems,” warned mayor Bikash Ranjan Bhattacharyya, while inaugurating a water harvesting system at the Diamond Beverages plant, a bottling facility in Taratala, last week.

According to the mayor, a recent study carried out by the CMC shows that mainly people from higher and middle-income groups in the city waste water. “I do not want to cause panic, but there may be increasing cases of subsidence, as well as intrusion of pollutants like arsenic, in groundwater because of its random withdrawal,” he said.

S.P. Sinha Roy, a former member of Central Ground Water Board and a consultant for the Taratala project, agreed. “The groundwater level in the city has gone down significantly. In the Taratala area, the level has gone down by 12 to 15 ft. In some areas, it has gone down by about 30 ft. We need to take control of the situation soon,” he said.

The chairman and managing director of the plant, N.R. Goenka, claimed that the rainwater harvesting system would recharge the water table — which is 150-200 ft below the surface — with 12 lakh litres of rainwater annually.

“Currently, the project plans to utilise about 5,500 sq m of the plant terrace to harvest rainwater,” said an expert.

Goenka also said that groundwater usage is being cut down for producing soft drinks. “A few years ago, we required 5 l of water to produce a litre of soft drinks. Now, it has been reduced to 3 l. We hope to cut down on the water usage further” said Goenka.

“The CMC has been claiming for ages that it would come down hard on water wastage and make rainwater harvesting compulsory but nothing has been done yet,” said an environmentalist, adding that around 30 per cent of the piped water supply of the CMC is regularly wasted because of pipeline problems.