SINGAPORE - National water agency PUB will look into enhancing treatment processes after some homes reported that boiled tap water gave off a pandan smell earlier this week.

Screening technologies at present do not allow for the detection of trace amounts of the organic compound tetrahydrofuran (THF), which is responsible for the pandan-like odour, PUB said on Facebook on Friday (July 24).

On Wednesday, some households in Pasir Ris, Yishun and Tampines reported a pandan-like smell in their water.

PUB subsequently said this issue was traced to water imported from Malaysia.

It said on Friday that it is working with the Malaysian authorities to identify the source of the THF found in the water system.

The agency clarified on Friday that while water from Malaysia is treated at PUB's waterworks in Johor before it arrives in Singapore, similarly stringent water treatment and quality monitoring processes apply.

PUB also said that THF, which is highly soluble, has a low boiling point of 66 deg C, causing it to vaporise upon boiling, giving off a distinctive floral scent.

It noted that there are currently no international standards for THF levels in drinking water, although Minnesota in the United States has health-based guidelines of 600 parts per billion.

PUB's laboratory tests found trace levels of less than 10 parts per billion of THF in the water supply.

In Friday's update, the agency also noted that it has completed the flushing of service reservoirs, the transmission and distribution network and water tanks to remove THF traces from the system.

"The quality of water supply across the island remains consistently within normal and acceptable range. We have also been testing incoming water supply from Johor and are satisfied that it is now of good quality," it noted, adding it will no longer provide water bags to affected households as the tap water is safe for consumption.

The full replacement of affected water in the network means there should no longer be any smell although PUB noted that any "lingering" odours are "likely due to remnant water in house pipes".

Customers are advised to run their taps for five minutes to eliminate this.