Pipes carrying water to the city from Palta in North 24-Parganas are being covered with “mild steel jackets” to prevent damage during the ongoing Tallah bridge construction.

Water from Palta is stored in the Tallah tank. Eight pipes supply around 230 million gallons of water every day from the 111-year-old reservoir to large parts of north, central and south Calcutta. Six of the pipes run to the east of where the old Tallah bridge stood, and one each to the west and north. A ninth pipe is on standby.

The Tallah reservoir gets its supply from Palta, 21km north, through three pipes.

Engineers from the Calcutta Municipal Corporation have identified seven of these pipes, including the three that bring water from Palta, to be covered with mild steel jackets.

Jacketing will involve putting an encasement of steel around the pipes to protect them from external damage.

“These are very old pipes. During the construction of the new Tallah bridge, these pipes are likely to be subjected to heavy vibrations underground. As a result, they could develop cracks,” said a senior CMC engineer overseeing distribution of drinking water across Calcutta.

“By wrapping a mild steel jacket on each of them, we will prevent any injury to the outer walls of these pipes that may result in leakages,” he said.

The CMC produces 440 million gallons of potable water every day to cater to around 45.6 lakh people. A little over half the volume is routed through the Tallah tank, which was inaugurated in 1909.

Engineers said they had identified patches on the underground water pipes that were vulnerable to cracks and needed to be wrapped with a mild steel jacket.

A team of engineers has collected details of the alignment of the pipes from the PWD, which is executing the Tallah bridge construction project.

These pipes are from the British era and their diameter varies between 42 and 68 inches, a PWD official said.

“Unless the jacketing work of the pipes from Palta is completed, we can’t begin our work of building two piers on the Dunlop-end of the flyover. We have set March as the deadline for finishing this work,” said a senior PWD official.

The proposed Tallah bridge, which will connect large parts of north Calcutta including Dunlop, Sinthee, Chiria More with Shyambazar, will have two spans on either side of the flat deck in the middle. These two spans, each measuring about 280 metres in length, will stand on 12 pillars.

The deck in the middle, about 230 metres in length, will stand on a set of six pillars. The arm of the bridge that will go towards Chitpore railway yard, spanning around 250 metres, will stand on a set of two pillars.