The authorities are looking into the possibility of sampling used water for pathogens as an early warning system for outbreaks like Covid-19, The Straits Times has learnt.

National water agency PUB said it is aware of research findings in the Netherlands on sewage surveillance and its potential in sounding an early warning alarm for outbreaks.

But Mr Maurice Neo, PUB's director of the water reclamation network, noted that this research is still in its early stages. He added: "PUB is also working with local and overseas researchers to develop it further and will continue to keep abreast of the latest global developments and research on Covid-19."

In March, Dutch researchers from the KWR Water Research Institute published a scientific paper pending peer review on pre-print site medRxiv.

The researchers said the virus causing Covid-19 had not been detected in samples collected across eight sites - including Amsterdam, the Hague, Utrecht and Amsterdam Airport Schiphol - before the first case was reported in the Netherlands on Feb 27.

But on March 5, a specific fragment of the viral's genetic material was detected in the sewage of five sites. Later that month, the same fragment was found in the sewage at six sites.

The authors noted that it was unlikely that wastewater will become an important transmission pathway for coronaviruses like Sars-CoV-2, the virus that causes Covid-19.

But the increasing circulation of the virus in the population will increase the virus load in the sewer systems, the researchers noted.

More research could help determine if sewage surveillance could complement current clinical surveillance, which is limited to Covid-19 patients with the most severe symptoms, they added.

Australia this week also rolled out a programme of sewage testing to detect clusters.

The National Environment Agency (NEA) said researchers from its Environmental Health Institute are studying the virus causing Covid-19 in wastewater here.

"As the research is still in its early stages, time is needed to conduct more detailed analysis and to draw useful results. More information will be provided when ready," NEA said.

Currently, used water from households is not sampled for pathogens as it undergoes treatment at the water reclamation plants. Water is tested after treatment to ensure it is safe for consumption or discharge.

PUB regularly monitors drinking water quality, right up to customers' taps, to ensure it complies with the standards stipulated by governmental regulations. Mr Neo said water quality is also well within the World Health Organisation's guidelines for drinking water.

Water experts whom The Straits Times spoke to were assured of Singapore's drinking water quality.

Professor Asit Biswas, a distinguished visiting professor from the University of Glasgow and chief executive of the Third World Centre for Water Management in Mexico, said: "Singapore has a robust wastewater treatment system which will take out all viruses, including this coronavirus. There is thus absolutely nothing to worry about."

He added that measurement instruments were also sensitive enough to detect drugs and disease vectors, including the coronavirus, in wastewater.

But this information may be of limited value. "While we can detect them, it does not provide any information on who are the specific individuals infected, or how they can be identified," said Prof Biswas, adding that knowledge of the novel virus was ever-changing.

"It is thus one piece of additional information which should go into overall considerations," he said.

But Professor Shane Snyder, executive director of the Nanyang Environment and Water Research Institute at Nanyang Technological University, said he strongly advocates the use of wastewater-based epidemiology - a process that some countries have already started - for Singapore.

Smaller and densely populated countries have great advantages in implementing such an approach, he said.

Prof Snyder acknowledges that many challenges and knowledge gaps still exist in the field, but the increasing number of countries investing in this approach highlights the technique's potential and benefits.

"For Singapore, I believe wastewater-based epidemiology should be considered for monitoring the extent of infection in general, such as at our centralised wastewater treatment facilities, and to pinpoint new outbreaks," he said.

This could include monitoring sewage from specific Housing Board blocks, dormitories and condominium complexes, he said.