The contamination crisis stemming from the Williamtown Air Force base is now impacting on the Hunter's water supply, with Hunter Water losing access to 1.5 billion litres in the Tomago Sandbeds.

Hunter Water has three pump stations inside the Environment Protection Authority's investigation zone of the sandbeds, and has chosen to not use them until New South Wales Health deems it safe.

Hunter Water said water has been sampled at several points in the sandbeds and the chemicals have never been detected.

But interim CEO Jeremy Bath said it is vital the Defence Department moves quickly to remediate the sandbeds.

"Hunter Water is calling on the Department of Defence to move urgently to remediate the Tomago Sandbeds," he said.

"So hopefully that remediation can be successful, and we can have the return of that 1.5 billion litres of water, which we can then use in times of a drought or should we for some reason lose access to Grahamstown Dam."

Mr Bath said the water supply in the Tomago Sandbeds is crucial during times of drought, and also if the organisation was to ever lose access to Grahamstown Dam.

"It represents about two per cent of the total water available to Hunter Water," he said.

"It's about 10 per cent of the water that Hunter Water typically has access to within the Tomago Sandbeds.

"That water is crucial when the Hunter suffers a drought or should we for some reason lose access to Grahamstown Dam, which could be something as simple as the outbreak of blue green algae."