Brass fittings are the key source of lead leaching at the Perth Children's Hospital, rather than the "dead leg" in the ring main, the state government says.
The West Australian government has released a technical report into the ongoing issue, partly disputing the findings of an independent report from the Building Commission last month, which found the most likely source of contamination was both the ring main pipes and the brass fittings.
Treasurer Ben Wyatt said the dead leg water pipe, which was removed as a precautionary measure in September, was unlikely to explain the ongoing lead problem.
"It's unlikely to have been the dead leg to have been releasing through the sludge into the water prior to it being disconnected," he told reporters on Wednesday.
Mr Wyatt said there were also elevated levels of lead, zinc and copper in the dead leg, but not in the hospital.
He said the Jacobs Report, developed by the Department of Treasury's hydraulic engineering adviser, was commissioned specifically for the water issue, while the Building Commission did not have all the information.
The Jacobs Report concluded that leaching from brass fittings within the hospital "potentially exacerbated by dezincification" was the source of elevated lead levels, attributing it to water sitting in the hospital's pipes for months.
Health Minister Roger Cook said phosphate treatment to reduce lead levels would begin this week.
After the lead contamination is treated and the Chief Health Officer declares the water safe, the full commissioning will begin, which Mr Cook estimated could take up to 14 weeks.
He also insisted there was no risk to the public or staff at the wider Queen Elizabeth Medical Centre precinct.
Contractor John Holland has previously claimed lead came into the hospital from an outside source.
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