A decision on whether to press ahead with a full-scale water recycling plant could be made within months after the completion of a landmark trial to pump treated sewage into Perth's groundwater.
The Departments of Health, Water and Environment and Conservation have begun assessing the results of the $50 million trial, which wrapped up after three years on December 31.
A recommendation about whether the State Government should expand the trial into Perth's next major drinking water source is expected as early as April or May.
With strong cross-party political support, a full-scale plant providing at least seven billion litres of water a year could be operating by next year if it wins approval.
The project, which was allocated $108 million over four years in last May's State Budget, would be built in modules and could have an eventual capacity of 28 billion litres a year.
Under the trial technology, sewage from Beenyup is treated to a drinking standard before being pumped into groundwater, where it undergoes further natural treatment as it percolates through the aquifer over several years.
Water Minister Bill Marmion, a supporter of the technology, was upbeat about the results from the trial, saying they had been "excellent".
He said more than 70,000 samples were taken during the trial and all had met "stringent health and environmental guidelines".
Health Department water unit manager Richard Theobald echoed the comments, saying health regulators looked for 18 potentially harmful agents in water samples and none had been found during the trial.
Mr Theobald said the trial had also positively answered the key question about whether the Water Corporation was competent to run such a project.
"The science has been extensive," he said.
"It is as good as we can get it - I can't say any more than that.
"And so I'm very confident that it's right."
Mr Theobald said any expansion would be subject to stringent checks. DID YOU KNOW? 70,000 The number of water samples taken during the trial