The pandan smell emitted from boiled tap water, due to an organic compound called tetrahydrofuran (THF), has been isolated. 

According to an update from the Public Utilities Board (PUB) – the National Water Agency – on Thursday (23 Jul), it has also flushed out the affected network pipes and water tanks. The water was subsequently replenished with water produced by local waterworks. 

It also wrote that its officers have collected more water samples from customers’ taps and Singapore’s water mains for further analysis. 

“(The officers) have also conducted on-site tests and will (continue) to take new samples today to continue the tests.” 

PUB assured that the water supply is safe for consumption directly from the tap or boiled. 

The update concluded that “customers should not detect any smell from tap water freshly supplied from our waterworks”. Should any lingering scent persist, it could be due to “remnant water remaining in house pipes”. It can be cleared by running the tap for five minutes to flush out the water. 

The board expects the issue to be fully resolved by the end of the day. 

Residents complained about pandan smell from boiled tap water

Residents living in Pasir Ris, Tampines and Yishun provided feedback to PUB about the scent they had detected. On Reddit, some residents living in other areas such as Punggol, Bedok, Tanjong Pagar and Bukit Timah have claimed their water supply produced the pandan smell and taste as well.

PUB subsequently conducted laboratory tests on water samples taken from these residences. Its preliminary investigations were released on Wednesday (22 Jul) where the agency discovered trace levels – small amounts – of THF in the water – less than 10 parts per billion (ppb). 

The affected water supply seems to be from the imported water from the Linggiu Reservoir in Johor, said a PUB’s spokesperson. The river is a major source of water for Singapore.

Malaysian media had carried reports on Thursday (16 Jul) that residents in Johor Bahru have also detected the pandan smell in the tap water. 

The spokesperson added: “PUB has taken immediate action to isolate the affected water pending further investigation, and is working with the Malaysian authorities on this matter. We expect that this issue should be resolved by Thursday (23 Jul).”

Tetrahydrofuran and its trace levels 

The THF compound is a clear, colourless and volatile liquid that is used to create the solvent for polyvinyl chloride (PVC). PVC plastic is used in things such as indoor plumbing and film casting. 

Other uses of the solvent include cleaning agents and producing nylon. 

Less than 10 parts per billion (ppb) were reportedly found in the test sample that PUB conducted on. Ppb is a unit used to describe trace levels of contaminants in drinking water. 

10ppb is like 10 cents out of US$10 million. It basically means 10 micrograms (mcg) per litre of water. 10 mcg equals 0.01 millilitre. According to the New Hampshire Department of Environmental Science, the healthy limit for drinking water is at or below 154ppb. The healthy level for airborne is at or below 200ppb, according to the US National Centre for Biotechnology Information.  

If consumed above health levels, it may cause serious eye irritation, respiratory irritation, nausea, dizziness and headaches. 

Naturally occurring minerals discoloured water at Tekong Basic Military Training Centre in 2019

Discoloured tap water was reported at the Basic Military Training Centre (BMTC) in Pulau Tekong on 20 November 2019. 

Two months later on 3 Feb 2020, Environment and Water Resources Minister Masagos Zulkifli said in Parliament that the discolouration was caused by naturally occurring minerals that accumulated in the water supply network over time. 

“The pipes serving the BMTC were churned up, thus affecting the appearance of the water. The tap water turned clear after (the) flushing of the water supply network,” said Mr Masagos.