Black particles in HK tap water found to be asphalt and resins: Gov't

Government tests confirmed that black particles found in Queen’s Hill Estate’s tap water are asphalt mixed with resins, Director of Water Supplies Roger Wong Yan-lok announced, following a week of concern among residents.

Last Friday, residents of Queen’s Hill Estate and Shan Lai Court in Fanling began to raise concerns over abnormal tap water quality, reporting black particulate matter flowing from their faucets.

Speaking to reporters on Thursday, Wong said the resin likely came from protective layers of gate valves flaking off, based on its physical characteristics and chemical composition.

While the asphalt, a banned substance for pipe inner coating, probably came from residues left in the pipes even before the Water Supplies Department installed filters in 2022, he added.

Wong acknowledged residents’ worries and assured the public that the materials pose no health risks and fully comply with Hong Kong’s drinking water safety standards, referencing a 2020 asphalt safety study commissioned by the WSD.

Researchers boiled 10 grams of asphalt in three liters of water and found that it didn’t release any toxic substances. Wong noted that the amount of sediment in the estate’s tap water was just a tiny fraction, only one part in 3,000, of what was tested in the study.

“[We] will intensify pipe flushing operations to remove any remaining asphalt residues and enhance our sampling efforts, conducting regular daily tests until no black particles are detected in the water samples,” he said.

Similar sediment discovery happened in 2022, when public housing tenants moved into the vacant residential building, formerly used as a Covid-19 isolation facility, according to the water supply director.

Wong said as residents moved in and began to use water, this triggered a sudden water flow, and had likely dislodged long-accumulated deposits within the pipes and pushed them into the supply network.

As a precautionary measure back then, the WSD conducted thorough tank and system flushing at that time and installed 0.1 millimeter filters.

Wong suggested that the recently detected particles were likely residual deposits that had remained in the pipes before the filter instalment.

However, he did not say where the asphalt originated, as the government had stopped using water pipes with asphalt as an anti-rusting inner coating and replaced them with those coated by epoxy resins since 2005.

(Cheng Wong)