Water levels at storages supplying the Sydney metropolitan area are sinking amid a lack of rain and rising consumption, bringing the prospect of a restart of the Sydney Desalination Plant.

The total storage levels for the Sydney region are running at about two-thirds full, with the desalination plant set to be turned on to supplement the water supply when capacity drops to 60 per cent, according to WaterNSW.

Cordeaux Reservoir's water levels have fallen by more than half in the past 12 months. Credit:Nick Moir

"All Sydney storage levels have fallen as water is used to provide for Sydney’s water supply, while record low rainfall in catchment areas [has resulted] in minimal replenishing inflows," a WaterNSW spokesman said.

"The absence of significant rainfall forecast and the extremely dry catchments means, unfortunately, there is little prospect of respite statewide in the short term."