Lawmakers on Saturday urged the government to do more to safeguard water quality amid concerns about black flecks found in tap water at two Fanling housing estates.

Chief Executive John Lee had on Friday told officials to form an expert group to look into the freshwater supply at Queen's Hill Estate and Shan Lai Court, and replace 400 metres of steel pipes where the bitumen coating is believed to have flaked off.

Speaking on a radio programme on Saturday, New Territories North lawmaker Edward Lau welcomed the government's decision to replace the aging pipes, saying this could reassure affected residents.

He also urged the government to set a timetable to replace some 700-kilometres of water pipes across the territory that are also lined with bitumen.

Technology and innovation sector lawmaker Duncan Chiu, meanwhile, said the authorities should explore the possibility of installing smart devices inside pipes for more effective monitoring.

"We can [use] mini robots or inspection machines to check on the water quality and leakages. We now mainly use these for inspection purposes, but not for holistic management of all the pipelines in Hong Kong," he said.

"I think that involves investments, and of course, debates on whether that's the best use of public budgets, public funding... We have to really balance the need and the investments in these," he added.