Large parts of Calcutta remained submerged on Thursday because several pumping stations that drain out water from the city remained unoperational following power outage.

Calcutta received more than 200mm rain on an average across the city on Wednesday and more than three-fourths of the precipitation happened between 5pm and 7pm, officials of the Calcutta Municipal Corporation (CMC) said. They said such heavy rainfall was bound to keep streets waterlogged for a long time.

The drainage pumping stations in many areas could not work during the storm and till well past midnight as there was no power supply, a civic official said. “Normal services could resume only on Thursday morning.”

The official said portable pumps had been kept ready in many low-lying pockets but “operating them in the dark was very difficult”.

“We were ready but power supply had to be cut off for a long time and our operations got delayed a bit.”

The waterlogging and the heavy rain meant water entered many houses, especially in low-lying areas.

Many houses have their underground water reservoirs in such locations that water seeped in. “The contaminated water should not be consumed. People should use this water only for flushing in the toilet. It is better to collect tap water from the CMC’s taps to bathe, drink and cook,” said a public health professional.

A CMC official said one of the ways to disinfect underground reservoir is to mix 500ml of sodium hypochlorite solution with 1,000 litres water. “This will disinfect the water but will not remove the foreign particles that have seeped,” the official said.

“The reservoirs where run-off water has entered must be cleaned before the water is used for drinking or cooking,” the official said.