Hunter Water will begin drawing water from the Tomago sand beds to provide additional security for the region's dams, which have fallen to their lowest levels in 13 years.
The sand beds, which comprise of a 109 square kilometre catchment, are used as a back-up water supply that can provide 20 per cent of the Lower Hunter's drinking water during times of shortfall.
The region's combined water supplies stood at 67.7 per cent on May 20, down 0.7 per cent on the previous week.
Level 1 water restrictions will be introduced in mid-August if present conditions continue.
Hunter Water chief investment officer Darren Cleary said the Tomago sand beds were a critical part of the water security strategy for the region.
"During dry periods, there comes a crucial time when we need to start drawing water from the sand beds, because if we leave it too long, the water simply won't be there later in a drought," he said
"The safety of our drinking water is paramount. We've done a lot of work over decades to understand how the sand beds operate and how the water flows. This includes extensive water quality testing.
"When we look to use the bore fields within the sand beds as part of our water supply, we are extremely rigorous in the way we test the water to make sure it is safe for drinking. We routinely monitor the water at the borefields, then as it arrives at the treatment plant and again before it goes to our customers' homes."
Water will not be drawn from bores near the near the Williamtown per-and poly-fluoroalkyl substances (PFAS) management area as a precaution.
"Hunter Water has the ability to choose which bores are used and which are not when drawing water from the sand beds. We've isolated bore stations 7 and 9, which are located inside the Williamtown management area, as a precaution," Mr Cleary said.
"Our customers can have confidence in the controls that have been put in place to ensure their drinking water remains safe and meets the guidelines," said Mr Cleary.
Water was last drawn from the sand beds in 2015.
Hunter Water does not operate the sand beds continuously due to the high costs involved in treating the water.
Water from the sand beds contains naturally higher levels of iron and the mineral manganese. These elements are difficult to remove and can cause discolouration.
"Discoloured water is not a health issue. If customers experience discoloured water, we recommend they first try turning their tap on full for a few minutes to clear the pipes," Mr Cleary said.