Trace amounts of hydrocarbons – the kind of compounds used in anti-mosquito oil – were found in the tap points of some residents’ homes in Ang Mo Kio, national water agency PUB said on Friday.
The contaminant was discovered when a resident on the sixth floor of Block 635 Ang Mo Kio Avenue 6 alerted PUB last Monday that his tap water gave off an oil-like odour.
The Ang Mo Kio Town Council responded by flushing the block’s rooftop water tanks last Monday and Tuesday.
These tanks supply water to flats from the sixth to the 12th floors.
A PUB spokesman said: “Water samples were collected from PUB’s water mains and the resident’s tap points on Jan 13 for analysis.
“Lab tests showed that water from the mains was of good quality, but that from the resident’s tap points contained trace amounts of hydrocarbons, compounds which could be found in anti-mosquito oil.”
Hydrocarbons, compounds made of carbon and hydrogen, are the main components of petroleum and crude oil. This type of anti-mosquito oil is usually used for fogging or application in drains to prevent mosquitoes from breeding.
Last Wednesday, the Ang Mo Kio Town Council engaged a plumber to wash and chlorinate the water tanks to remove any remaining traces of hydrocarbons.
The PUB also 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,” the spokes-man said.
The Sunday Times understands that the water which PUB supplied through the pipes, or water mains, was of good quality, but the water was then stored in tanks which had contaminants.
Stored water is supplied to residents’ taps when needed.
In December 2018, the Ang Mo Kio Town Council had workers clean the water tanks and pump room after a resident found a worm in the tap water.
PUB said town councils are responsible for maintaining and cleaning water tanks at Housing Board blocks. They must also have licensed plumbers regularly cleaning and disinfecting the tanks before certifying them safe for storing drinking water.
The PUB spokesman noted that all town councils receive circulars on the proper maintenance of their water service installations, including water tanks and pumps.
“These circulars also contain information on precautions to take during fogging operations, such as avoiding the spraying of insecticides – such as anti-mosquito oil – near water tanks, and to properly seal or cover all water tank openings, overflow pipes and drain outlets so as not to affect the safety and quality of water stored in the tanks,” he said.
The PUB website states that tap water quality is monitored continuously throughout the year.
It has also established a comprehensive and robust sampling and monitoring programme to ensure water quality from source to tap.
Online sensors monitor water quality at each stage of the treatment process and service reservoirs. More than 450,000 tests are conducted annually on physical, organic, inorganic, radiological and microbiological parameters.