The Water Corporation has urged people to use less of Perth's dwindling water supply after a dry start to winter has left the city's dams on track to record their lowest ever inflows.

Ben Jarvis, the corporation's water efficiency manager, said just five billion litres - or enough water to supply Perth for five days in summer - had flowed into the dams this year.

The figure is equal to the worst result recorded this late in the year and leaves Perth's dam levels at less than 30 per cent of capacity and holding barely 70 billion litres of usable water.

Each year, the city uses about 300 billion litres of scheme water.

Mr Jarvis said though he was hopeful the dam levels would recover if more rain fell over the rest of winter and into spring, the dramatic drop in inflow was alarming.

"If we hadn't built the two desalination plants we would be by far in the worst position we have ever been - there would be no water left in the dams essentially," he said.

"Our worst year ever was 2010 when we got 13 billion litres of inflow across our entire 13 dams and at the moment we're on that same sort of path.

"Of course, there's a long way to go. You can't see what we're going to get but it's certainly not a good start at all.

"Gone are the days when we would get 400 billion litres of inflow into the dams."

As the corporation pleaded with householders to reduce their water consumption on the back of the figures, the Weather Bureau warned the dry weather was set to continue.

In its daily statement yesterday, the bureau said Perth had recorded 168.2mm of rain this winter compared with 246.2mm over the same period last year.

Perth's long-term winter average is 478.7mm.

Neil Bennett, the bureau's regional manager, said: "July is now panning out to be very much below average and very concerning."

He said the outlook for the remainder of winter was also dry.

"Any rainfall we get from now has to initially soak the catchments before it starts to flow into the dams," Mr Bennett said.

"The thing that's happened that we can be optimistic about is that the trend of the past 30 years suggests the rains start later but finish later."

Despite the lack of run-off, Mr Jarvis said the corporation's decision to move away from dam water meant it was unlikely people would be hit with restrictions this year.

"It's what we've expected and what we've planned for," he said.

"That's why we built the first desalination plant and the second desalination plant and are currently expanding that.

"It's why we're putting our efforts into reducing per capita consumption and it's why we're progressing a lot faster in the recycling space."

In May, the State Government allocated $108 million over four years in the Budget for a plan to turn highly treated sewage into drinking water.

The West Australian

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