Water supplies director Roger Wong also said the water supplied to Queen’s Hill Estate and Shan Lai Court meets safety standards.
He announced the government test results a week after residents complained about impurities.
In a media briefing, Wong said from the colour and chemicals of the samples tested, officials believe that the resin found was protective coating that peeled off from the valves.
As for the bitumen, the water supplies chief said the government had used the material as coating for water pipes until it switched to resin in 2005.
He revealed that in December 2022, officials found similar particles in the water as residents started moving into Queen’s Hill Estate after it had been used as Covid quarantine facilities.
“At that time, we flushed the pipes, and after that, we installed a very fine-grained filter, so as to screen out all the black particles or other sediments that may move into the internal plumbing system,” Wong told reporters.
He said the residue particles had likely become finer over time and were likely washed up then because of a high amount of water flow, which might have happened again in the past week.
“We frequently cleansed the filter and did not find any signs of black particles. So we deduce that the black particles or the sediments may be moved or flowed into the internal plumbing system before the filter is installed.”
Wong reiterated that water at the two estates is safe to drink, as bitumen is insoluble but not harmful to humans.
He also said according to previous testing by a government-appointed consultant, no carcinogenic substances were released after water containing bitumen is boiled.
Wong vowed to beef up cleaning of the pipes, adding that water samples will be tested every day until freshwater supply is free of black specks.
