The Government today said the water quality of Queens Hill Estate and Shan Lai Court, Fanling, meets the city’s drinking water standards, and the bitumen found in water samples taken from the two estates is not harmful to the human body.

The Water Supplies Department (WSD) and the Housing Department (HD) outlined their follow-up work on the incidents where sediments were found in the drinking water at Queens Hill Estate and Shan Lai Court.

A working group was set up immediately to check water supply pipes, clean water tanks, install filters, conduct daily testing on water samples continuously. Samples of sediments were also sent to the Government Laboratory for testing.

So far, all water samples have complied with the Hong Kong Drinking Water Standards, including the Rapid Toxicity Test (light emitting bacteria) and Carcinogenic Benzo(a) pyrene for testing carcinogens. All water samples tested negative for these two parameters.

Furthermore, the WSD also conducted traceability work and passed 126 samples of materials collected from each block in the estates for the Government Laboratory's testing on June 3. Preliminary test results indicated that most of the samples consist of bitumen mixed with resin.

The WSD explained that bitumen was commonly used as a protective coating to prevent rust inside steel water pipes around the world in earlier years. It is an inert material and is insoluble in water.

According to experts, bitumen will not release materials harmful to the human body after mixing with water. In other words, even if drinking water has come into contact with water pipes coated with bitumen, the relevant water quality will still comply with drinking water standards.

However, after prolonged use of water pipes, bitumen coating is prone to spalling, which is not durable and affects the clarity of drinking water and people’s perception. Hence, for water supply pipes laid after 2005, durable epoxy resin-coated steel pipes had been in use instead.

As to whether drinking water containing bitumen will affect health, the WSD commissioned an expert consultant in 2020 to conduct an experiment by boiling 10g of bitumen in three litres of hot water. The result confirmed that no toxic substances were released.

Currently, the sediments (bitumen) in the water samples taken from Queens Hill Estate are three-thousandth of the amount used in that experiment, on a per-litre basis, so citizens need not worry even if they have consumed drinking water with bitumen.

Records revealed that the relevant pipes in the two estates do not contain bitumen materials. Furthermore, the WSD installed screen filters outside the Queen’s Hill Estate in December 2022, which can block substances larger than 0.1mm in diameter.

Since then, the WSD has been conducting weekly inspections of the filters’ condition.

After receiving a report on the water quality incident on May 30, the WSD checked the filters again and confirmed they remained intact with no damage.

Given that the sediments found within the estate exceeded 0.1mm, along with the discovery of a section of steel water pipe upstream that was coated with bitumen on the inner wall, the WSD reckoned that the sediments are likely residual bitumen materials that flowed into the Queens Hill Estate pipes from the aforementioned steel pipe before December 2022. 

As for the resin material, its presence in the water is likely due to the flaking off of the protective layer from water valves.

In the meantime, the HD continues to install additional filtering facilities with a density that can block impurities with a diameter of 0.1mm or larger on the existing facilities in Queens Hill Estate and Shan Lai Court.

Apart from the additional nine filters that have been installed since the report of the incidents, 13 new filters were added today, seven at Queens Hill Estate and six at Shan Lai Court.

The WSD will continue to probe the incidents and submit an investigation report to the Drinking Water Safety Advisory Committee for review.