SINGAPORE - Singapore has ramped up local production of water to meet demand after some water from Malaysia had to be "isolated" following reports from some households here about an unusual scent of pandan in boiled tap water.
The cause of the scent is an organic compound known as tetrahydrofuran (THF), which is commonly used as a solvent in industries.
National water agency PUB said its investigations have traced the source of the issue to water imported from Malaysia.
In a Facebook update on Thursday (July 23), PUB said it has "isolated" the affected water, and that production has been ramped up at waterworks in Singapore.
"We also took extra precaution to flush out the affected network pipes and water tanks, and replenished them with water produced by our local waterworks," said PUB.
"We ramped up our local production (on Wednesday)," it added in the statement, although it did not provide details on how much local water production was ramped up by.
The Johor River in Malaysia is a major source of water for Singapore.
But the Republic can also count on its three other taps - desalination, treatment of used water and rainwater collected in Singapore's 17 reservoirs.
The Straits Times had reported on Wednesday that a number of households in Singapore - such as in Pasir Ris, Yishun and Tampines - had noticed an unusual scent of pandan in boiled tap water.
Laboratory tests of water samples taken from affected homes and from water mains had found trace levels - less than 10 parts per billion - of the THF organic compound in the water supply.
This concentration is equivalent to dissolving two tablespoons of a substance in an Olympic-sized swimming pool, PUB said.
It added that THF is highly soluble and has a low boiling point but, due to the trace amounts present in the water in this incident, has no adverse impact on health.
The reports on the pandan-smelling tap water in Singapore follows similar reports from across the Causeway.
Malaysian media reported on Wednesday that residents in Johor Baru had also noticed the peculiar scent in their tap water.
In Thursday's update, PUB said customers should not detect any smell from tap water freshly supplied from Singapore's waterworks.
"Any smell could be due to remnant water remaining in house pipes," said the agency.
"This can be resolved by running the taps for about five minutes to flush out the water," PUB added, saying it will continue to monitor water quality closely.
Professor Shane Snyder, executive director of the Nanyang Environment and Water Research Institute at the Nanyang Technological University (NTU), said THF is difficult to detect in water, other than by its odour.
"THF does not absorb ultraviolet light and at the low concentrations found in PUB waters, it is not even detectable by normal general screening technologies," he said.
"In other words, it would be nearly impossible to detect through the online monitors that protect against major water quality upsets."
Prof Snyder also said that THF does not react rapidly with chlorine and is generally more challenging to remove during water treatment.
Prof Snyder said THF is not generally regulated as part of the drinking water laws, likely because it is not considered highly toxic.
"From every THF regulation and/or guideline I could find, the concentrations of concern are 10 to 100 times higher than the concentration of THF that PUB has reported," noted Prof Snyder.
"Thus, I agree that THF at the concentrations reported by PUB in the drinking water are not significant to human health."