The WA Government will spend $120,000 trying to fix lead contamination in the water pipes at the long-awaited new Perth Children's Hospital but will bill the contractor for the cost, Treasurer Ben Wyatt has confirmed.

Key points: The Government confirms practical completion of the $1.2 billion facility, which has faced significant delays, despite an ongoing lead issue

The Government confirms practical completion of the $1.2 billion facility, which has faced significant delays, despite an ongoing lead issue They will inject phosphate into the water pipes which will act as a barrier to the lead, with the cost billed to John Holland

They will inject phosphate into the water pipes which will act as a barrier to the lead, with the cost billed to John Holland The Health Minister hopes the facility will be accepting patients by August

The State Government today finally confirmed practical completion of the new $1.2 billion facility, which has been plagued by construction problems including asbestos contamination and, most recently, unsafe lead levels detected in the water supply.

The opening date for the facility has been repeatedly pushed back as contractor John Holland sought to rectify ongoing issues.

Mr Wyatt said the Government had assumed control of the hospital, and would spend $120,000 putting a phosphate solution through the water pipes, which he hoped would fix the contamination problem.

The Treasurer said having the hospital sit idle has been costing the state $6 million per month.

"This has been a long and somewhat frustrating process and an expensive process," he said.

"But the state has decided to expedite the conclusion of the construction of the children's hospital and to resolve outstanding lead issues, to issue practical completion, so the state can take control of the site.

"There are a range of remnant issues ... the lead is still at levels that the state is not satisfied ... meet the guidelines.

"Under the terms of the contract we can take practical completion and John Holland is still liable for the costs of any defects that need to be rectified."

Health Minister Roger Cook said he was hopeful patients could move into the facility by August, but the state's chief health officer would need to determine that lead levels were safe before the hospital could be fully commissioned.

Brass fittings to blame for lead scare: Government

Mr Wyatt said it was the Government's view the lead contamination was a result of the de-zincification of brass fittings in the pipes.

"We intend to go through a process of effectively injecting phosphate into the pipelines, that effectively acts a barrier," he said.

"Phosphate is already an approved water additive so that's something that we can introduce into the water pipes to resolve the lead issues."

Ben Wyatt (l) and Roger Cook. Mr Wyatt says the Government and John Holland remain in dispute over the source of the lead. ( ABC News: Eliza Laschon )

But he said John Holland still disputed the source of the lead was the brass fittings.

"Through the filtering process and replacing of pipes, there can no longer be any other source another than the potential zincification of those fittings," Health Minister Roger Cook said.

"The water coming into the hospital is fine."

Contractor John Holland declined an interview with the ABC, but issued a statement attributed to regional manager Lindsay Albonico, saying the company "noted with interest" the Government's comments.

"[We] look forward to speaking frankly and openly on the matter at the planned Commission of Inquiry into the PCH and other state projects," the statement said.

"Indeed we would welcome any independent review related to the construction of PCH.

"John Holland is fully accountable and transparent in respect to our management of PCH."

'Risky business': Nahan

State Opposition leader Mike Nahan said the Government was taking a risk in accepting the completion of the hospital.

"It is a very dangerous thing to take possession of a hospital, a children's hospital, that has lead in the water and you don't know really what the cause or source is," he said.

"The children's hospital is the canary in the mine and I think we might have to test more widely."

Mr Cook also criticised the $500,000 per month contract being paid to Capella Parking to manage unused parking bays at the hospital.

"It's an extraordinary arrangement isn't it? And that's one that the Commission of Inquiry will get to the bottom of, I'm sure," he said.

"I'd be very surprised if it didn't take a good, long, hard look at that particular one."