The water supply network in the city is awaiting a debacle with the 180-year-old pipeline between Palta and Tallah likely to burst any moment.

The steel pipe laid by the British in 1820 has outlived its estimated lifespan long back. According to the civic engineers, the wall of the five-ft diameter pipe has become thin due to corrosion and wear and tear and it can barely withstand the water pressure..

A crack in the pipe would disrupt filtered water supply on the stretch between Cossipore to Tollygunge. The 22-km long network caters to over 70 per cent of the 5.5 million residents of Calcutta.

“We are really worried about the condition of the pipe under BT Road. It should be have been changed much earlier. It’s a miracle that a pipeline nearly 200 years old is still distributing over 200 million gallons of filtered water,” said mayor Bikash Ranjan Bhattacharyya on Thursday.

Municipal commissioner Alapan Bandyopadhyay, working out a plan to refurbish the pipeline, said the scheme would cost over Rs 250 crore.

The Calcutta Municipal Corporation is planning to approach the Jawaharlal Nehru National Urban Renewal Mission for funds to refurbish the Tallah-Palta network.

Two technical options are open before the civic body, said chief engineer (water supply) Bibhas Maity, to ensure a steady supply of treated surface water from Palta waterworks to other parts of the city for the next 100 years.

The first option is to lay a pipeline between Palta and Tallah, via Kalyani Expressway, Durganagar rail station and VIP Road. The second option, which has found more takers in the civic body, is insertion of a steel pipe in the old pipe to reinforce it from inside.

If the second option is accepted, civic engineers said, the volume of water Tallah receives from Palta will drop and it will be hard for the water supply department to meet the city’s demand.

Hence, the civic body is considering the possibility of laying another five-ft diameter pipe under BT Road.

Acting on an order from the civic commissioner, chief engineer (water supply) and two former chief engineers conducted a preliminary survey on BT Road last week.