The Hong Kong government announced on Wednesday it was expanding water tests for lead to another 10 public housing estates to allay public fears about water safety.
But a source in the water works industry warned that the lead poisoning problem could be even more widespread.
The latest government move came after initial tests found excessive levels of lead in some water samples from three public housing estates - first at Kai Ching Estate in Kai Tak, and then Kwai Luen Estate Phase II in Kwai Tsing and then at Shui Chuen O Estate in Sha Tin.
A further water test, however, cleared Shui Chuen O after 10 samples from the estate were found to be clean.
The new round of tests will cover nine public housing estates - with a total of 24,000 households - completed after 2013, as well as Kwai Luen Estate Phase I.
The government found lead in water samples from two blocks of Kwai Luen Estate Phase II on Tuesday.
Asked why they were drawing a line at 2013, Secretary for Transport and Housing Anthony Cheung Bing-leung explained that the government has limited resources and also that Kai Ching and Kwai Luen were both completed after this time.
The government earlier tested seven places (including five public estates and two other buildings) for lead after the Kai Ching discovery. All the seven places' plumbing works were done by the same plumber as Kai Ching.
Cheung reassured the public that the additional tests were not being undertaken based on suspicion of the estates' water quality.
But an industry source being consulted by the government on the issue told China Daily the problem could be more widespread than expected.
The Housing Authority could make the situation worse by using chlorine to wash pipelines.
The source, who had examined the material used in one of the estates with tainted water, said tin bars with lead are widely used as soldering materials on construction sites. This is because they are cheaper than those without lead.
To avoid lead contamination at the source, the veteran plumber suggested the Housing Authority ban the use of tin bars with lead in the building of flats.
He further explained that a lack of skill in pipe cutting could leave wide gaps at joints, where soldering could result in larger contact areas with water.
This could then allow a high residue of lead to get into the water supply system.
The source said that the Housing Department uses chlorine to wash all pipelines before buildings are occupied.
hat could make the problem worse because chlorine erodes the tin bars and releases more lead into water.
Secretary for Development Paul Chan Mo-po said the government would remove pipelines and their soldered joints, as well as taps and other plumbing fixtures from Kai Ching Estate's water supply chain.
They would then be examined by government's task force, which is comprised of three experts and academics and several department heads.
The Housing Authority will also set up a task force today (Thursday) to review the overall construction process of public housing.
This includes quality checks on construction materials such as prefabricated parts and supervision of various construction processes.
Meanwhile, the Department of Health has arranged 550 people to have blood tests after receiving 981 inquiries in regard to the water scare.