The amount of water released from the state's dams into rivers will be halved this summer in the latest battle to save the resource after a parched winter.
The Department of Water said the decision would save four billion litres of fresh water - or the equivalent of the usage of 40,000 people for a year.
It comes as the dams supplying Perth stand at just 32 per cent full after the driest winter, and one of the driest years, on record.
That is the lowest level for the dams for this time of year in any of the past eight years.
The Water Corporation has urged Perth residents to try to save 60 litres a day during summer, in an effort to cut back on 13 billion litres and possibly avoid serious restrictions next summer.
Department of Water water resource management director Greg Davis said the decision to cut the amount of water released was made with regard to downstream users who relied on river flows for basic water supplies and businesses.
"With flow into dams this past winter being significantly reduced, we had to assess how much water we could release into catchments where there was already low stream flow," he said.
Users were being contacted to also ask them to reduce their take of river water by 50 per cent, and to use alternative sources where possible.
"This comes on the back of already low stream flow which means less available water," Mr Davis said.
The dams affected include Canning, Wungong, Serpentine, North Dandalup, Lower South Dandalup, Stirling, Harris, Samson, Harvey, Wellington, Logue Brook, Drakes Brook, Wokalup, and the Conjurunup Pipehead.
