Perth could get more than 100 billion litres of its future drinking water - the equivalent of a third of current supplies - from recycled wastewater, the State's water agency says.
A Department of Water blueprint maps out WA's water prospects as demand rises and rainfall declines.
Under a landmark decision in August, the State Government pushed ahead with plans for Australia's first full-scale water recycling plant in Perth's northern suburbs.
The $116 million move, which came after a trial and is due to be completed by mid-2016, will result in seven billion litres of highly treated wastewater pumped into an aquifer.
There it will undergo years of natural filtration before being pumped up and incorporated into scheme water for public consumption.
Although the Government has indicated the project could eventually be expanded to 28 billion litres, the department's report provides a clear picture of how far authorities want to go with the technology.
The department's role is to look after WA's water stocks and provide advice to the Government on source development.
It said Perth's water demand, as well as of that connected towns in Peel, the Goldfields and Wheatbelt, would double in that time and there was a shortage of new surface or groundwater sources.
The Water Corporation referred to its own modelling which suggested recycled wastewater could provide up to 115 billion litres a year by 2060.
By then, the corporation said, such a total would amount to about 20 per cent of Perth's drinking water needs.
Water Minister Mia Davies, while noting the estimates were long-term, said she was comfortable with the idea of Perth using so much recycled wastewater and believed the public would be, too.
She said other parts of the world faced similar challenges to Perth, but instead of injecting treated water into aquifers had to supply it directly to households.
Shadow water minister Dave Kelly said Labor supported "aquifer recharge" in principle but the Government needed to show projects were cost effective and had public backing.
The city's dams are 27 per cent full at almost 173 billion litres, which is marginally more than this time last year.
However, the true state of storage levels is much worse because the last 110 billion litres of dam water is unusable.