The expansion of Western Australia's second desalination plant could be put on the backburner forever, Water Minister Bill Marmion says as the government seeks to speed up a trial of recycled drinking water.

Mr Marmion has written to the Water Corporation asking whether a two-year sewage treatment trial could be fast tracked to meet the worsening water shortage facing Perth and the South West.

The trial was launched in November last year in which five megalitres of waste water is treated each day and pumped into the Gnangara aquifer near Beenyup.

Although the water has gone under intensive treatment removing bacteria and chemicals and mixed with existing groundwater, it won't be used for drinking supplies until the trial is finished and the government gives the go ahead for a full scale project.

Mr Marmion said he has been advised by the Water Corporation if they could speed up the trial it would still take 18 months to get all the necessary infrastructure in place.

"I would like to make sure we're ready if we can bring it on, but that does require a number of things to happen," he told reporters.

"One is we need to get community support behind the idea of actually pumping water into the aquifer and obviously we need Department of Health clearance that the water is safe before we could actually push the button."

He said the current trial was about gaging community support but would not say whether it was the sole factor in determining if the plan got the green light.

If the $50 million trial, jointly funded by the state and federal government, is a success it could end up treating 14 billion litres of waste water a year.

The move has raised questions about whether the expansion of the state's second desalination plant at Binningup, north of Bunbury, will happen.

The plant is due to come into operation later this year when the first stage is completed, providing about 50 gigalitres of water each year for the Perth metropolitan area.

But Mr Marmion, who would not say whether he preferred desalination plants over water treatment, said the second stage of Binningup desalination plant could be put off indefinitely.

"Stage two could be an option forever, it may not happen if you don't need it but it's one of those options we look at," he said.

Currently the dams, which supply water for Perth, Kalgoorlie, the South West, Wheatbelt and Goldfields regions, are only about 20 per cent full with one of the largest dams, the South Dandalup Dam, only eight per cent full.

So far this year Perth has only received about 100 millimetres of rainfall.
The Urban Development Institute of Australia has thrown its support behind the plan, saying the Perth metropolitan area was running out of water and population expansion would only exacerbate the problem.

"Don't be fooled that the water situation isn't grim, the forecast rain this winter will do little more than wet the ground with very little flow in the catchment for dams," Ms Goostrey said.

"New developments are far more water efficient but we're now struggling to get bore water licenses to keep public open spaces green.
"It makes sense to top up the Gnangara water mound as part of a sustainable water strategy."

Ms Goostrey said the government was lagging behind the eastern states, and should have begun recharging WA's aquifers 30 years ago.