Taps in over 50,000 buildings in Ballygunge, Gariahat, Dhakuria, Kasba and Hazra went dry on Sunday following a 15-ft-long breach in the water main under Ballygunge Circular Road.

This was the second breach in an underground water main of the civic body in a month. On December 23, a vast area of north Calcutta faced water crisis after a water main under BT Road at Khardah sprung a leak.

The south Calcutta leak was detected on Saturday night when water started gushing from underground in front of Calcutta University’s Ballygunge Science College.

Soon after civic workers started digging the spot on Sunday morning, the area got flooded. Traffic on Ballygunge Circular Road was disrupted for an hour.

“It will take at least four days to repair the breach. We are taking some temporary measures and trying to restore water supply in medium pressure from Monday,” said mayor Sovan Chatterjee, who also looks after the civic water supply department.

The pipeline, of 48-inch diameter, feeds Kasba booster pumping station that supplies water across 20sq km in south Calcutta and the fringes.

A civic engineer said the inner wall of the pipe had to be jacketed as it had rusted and worn thin. There was no supply from the Kasba booster pumping station on Sunday as its reservoir could not be filled up because of the leak.

In some pockets such as Panchannagram, Tiljala, Natore Park, Panchanantala and Topsia, the civic body supplied water drawn from deep tubewells through a few roadside taps.

A senior engineer of the Calcutta Municipal Corporation said the only way to prevent frequent breaches in underground water mains was to replace the pipes that had been laid more than 20 years ago.

Rust has corroded the inner walls of the pipe and at some points the conduits have become so weak that they collapse under water pressure.

An engineer in the water supply department said Calcutta recorded the highest number of leaks in underground pipes in India.