A hydrologist from the University of Newcastle hydrologist says toxic chemicals from the contaminated Williamtown Air Force may have leached into Newcastle’s water supply.

Local water authority Hunter Water says its supplies are free from the dangerous firefighting substances believed to come from the Williamtown leak.

The group says a frequent testing regime over the past three years has found no positive readings for the chemicals.

But Hunter Water admits that it is not currently taking and testing water from the Tomago sandbeds - an underground water supply very near the site.

The University’s Professor Garry Willgoose has told reporters that these sandbed wells have been tapped during drought periods in recent years.

“This is an unusual chemical to test for, so I doubt Hunter Water has been testing for this on a regular basis,” he said.

“They do test the quality of water for all sorts of things.

“So it's conceivable that 10 years ago, in the midst of the drought, some of this may have gotten into the Newcastle water supply.”