Hong Kong authorities have been urged by lawmakers to disclose the locations of pipes lined with bitumen and to install sensors to monitor water quality after the substance was discovered in the freshwater supply at two public housing estates.

The government previously stated that 700km (434 miles) of water pipes, accounting for eight per cent of the city’s total water pipe network, had an inner protective coating of bitumen.

Lawmaker and engineer Lo Wai-kwok on Monday said the pipes in question should be replaced as soon as possible and their locations disclosed to the public to avoid a repeat of similar incidents.

“Although we have found the source of the bitumen and installed filters, the public are still worried,” he said on a radio programme.

“I think it is alright to reveal the locations of these pipes. Having these coatings does not mean they have an urgent issue and there are new technologies which can monitor their situations.

“It is necessary for the government to be open and transparent. The public are concerned about which residential buildings are affected by these pipes.”