The black particles found in the drinking water supply of some Taikoo Shing households on Saturday were believed to be bits of bitumen from the protective coating of water pipes, the Water Supplies Department (WSD) said on Sunday.

The department said in a statement that water samples were collected from affected households and the sump and roof drinking water tanks of buildings in phase four and five of the Taikoo Shing residential estate in Quarry Bay for laboratory tests, and results are pending. 

“Based on past experience, the black particles are believed to be bitumen protective coating in the water pipes,” the department said.

To facilitate pipe maintenance, the department had temporarily redirected the water supply near the residential estate on Saturday night and changes in water pressure may have disturbed sediment inside the pipes, the WSD said.

At the same time, investigations revealed damage to one of the filter facilities at Taikoo Shing's public water inlet, which may have allowed a small amount of sediment to enter the estate's public water pipes, causing particles to appear in some households' drinking water.

The WSD said it routinely inspects these inlet filters and the most recent check on Nov 3 showed no abnormalities. The damaged filter was repaired last night, and the department said it has strengthened pipe flushing in the affected system.

The department advised residents that if water has remained in pipes for some time, or when using taps for the first time each morning, they should let the water run until it becomes clear before consumption.

Water trucks have also been stationed on-site to provide temporary water supply for residents while the WSD has set up a service counter at the site, working with the property management office to assist in flushing water meters and to answer enquiries.