Around 100,000 residents in Kwai Chung and Tai Wo Hau in the New Territories are worried after people found their tap water had changed color and smelt of motor oil and kerosene.
The Water Supplies Department said no harmful substance had been found in water samples, Sing Tao Daily reported, but it said the smell could be linked to construction work at the Tsuen Wan Fresh Water Service Reservoir.
However, the department did not disclose what kind of chemicals could have caused the smell.
Water problems were reported at Kwai Chung Estate, Kwai Fong Terrace, the upper and lower Tai Wo Hau estates and some private residences in the area.
An old woman living in Kwai Chung Estate said she found the water smelt on Sunday and claimed that after using the water to cook noodles for dinner she had diarrhoea four times, Apple Daily reported.
Meanwhile, bottled water in nearby supermarkets had sold out.
Water tankers and wagons have been deployed to the affected residential estates to supply drinking water.