SINGAPORE - Trace amounts of hydrocarbons - the kind of compounds used in anti-mosquito oil - have been found in some residents's tap points in Ang Mo Kio, national water agency PUB said on Friday (Jan 17).

A resident living on the sixth floor of Block 635 Ang Mo Kio Avenue 6 had told PUB on Monday that his tap water gave off an oil-like odour.

The blocks' rooftop water tanks, which helped supply water to flats from the sixth to the 12th floors, were flushed on Monday and Tuesday by Ang Mo Kio Town Council.

Tests showed that while the water quality from the mains was good, the tap points contained amounts of hydrocarbons.

Hydrocarbons - compounds made of carbon and hydrogen - are the main components of petroleum and crude oil.

Ang Mo Kio Town Council engaged a plumber to wash and chlorinate the water tanks to remove any remaining traces of hydrocarbons on Wednesday.

PUB provided residents with water bags during the flushing and cleaning operations, which disrupted water supply to flats.

"We also monitored the quality of water supplied to the block over the next few days and can confirm that the water quality at tap points has returned to normal," a PUB spokesman said.

PUB said town councils are responsible for maintaining and cleaning water tanks at Housing Board blocks. They must also get plumbers to regularly clean and disinfect the tanks, before certifying them safe for storing drinking water.

PUB has also issued circulars warning that spraying insecticides too close to storage tanks during fogging operations can affect the quality of the water inside.