Tap water standards are back in the spotlight after traces of "forever chemicals" suspected of causing cancer were detected in a major dam.
Officials insist Sydney's water is safe to drink, despite detectable levels of synthetic chemical compounds known as PFAS being found at six sites.
They include the Warragamba Dam, the city's main reservoir.
The US Environmental Protection Agency recently found there was "no safe level of exposure" for two classes of PFAS chemicals in drinking water and they were likely to cause cancer.
That evidence will form part of a review run by Australia's water regulator, which has been expedited after April's landmark call in the US.
New guidelines are set to be issued for public consultation in October, before being finalised in April 2025.
Jeremy McAnulty from NSW Health said he didn't want to pre-empt the findings, but insisted Sydney water was safe to drink and met national standards.
"Sydney Water and other utilities regularly monitor for various parameters in drinking water to ensure it's safe and to identify risks and that's what's happening here," he said.
PFAS chemicals are found in everyday appliances from non-stick pans to clothing, insecticides and food packaging.
Once in the environment, they don't degrade further, earning them the nickname "forever chemicals".
Sydney Water testing conducted in June and published online without further notification shows one group of the chemicals was found in filtered water from Warragamba, albeit on the cusp of detectable levels.
Each result was below Australian drinking water standards, however those guidelines have been described as out of date.
All NSW drinking water catchments will be monitored for PFAS annually, while water-filtration plants at Katoomba and Blackheath in the Blue Mountains will be tested monthly.
That is because they had the highest levels of two potentially harmful chemicals.
"It's not above our guidelines, but just to be cautious we have chosen to get some additional monitoring for that system so we have a better understanding," Water NSW executive Fiona Smith said.
Victoria's Melbourne Water said over 99 per cent of its proactive tests came back with no detectable level of PFAS.
"For the few samples where PFAS was found, the maximum concentrations were well below health-based guideline values," a spokeswoman told AAP.
WA's Water Corporation said its "extensive" water testing program target-monitored PFAS and found no detections above Australian standards.
"We have robust source protection planning and management procedures in place to protect public drinking water source areas from all contaminants," a spokesman said.
The published results did not surprise or alarm PFAS expert Stuart Khan, head of civil engineering at the University of Sydney, who said people were more exposed to PFAS via other means.
"Even if you were to avoid the drinking water, it doesn't actually have a significant impact on your overall level of exposure to these chemicals, because you're being exposed through food, packaging, clothing, the entire planet around us," he said.
The US EPA has taken a hardline approach to the chemicals in drinking water, setting health-based goals to reduce exposure to zero and forcing water authorities to publicise PFAS levels and clean up contaminated supplies.
The US expects that over many years the regime will prevent exposure to the chemicals via drinking water for about 100 million people and prevent thousands of deaths.
