Water pipes in the Perth Children's Hospital will again be flushed, this time with iced water, in an urgent attempt to rid them of the lead contamination which is preventing the completion of construction.

The handover of the new $1.2 billion hospital has been delayed indefinitely while contractor John Holland tries to find and eliminate the source of elevated lead levels in the hospital's water system.

Treasurer Mike Nahan has been briefed by his department on the project and believes the contamination can be cleared by flushing the pipes.

"We've flushed gently. We've flushed with pressure. Now we're going to flush with ice," he said.

Dr Nahan said every part of the piping had been assessed in an effort to determine if building debris had made it into the system and was the source of lead levels in the water.

Tests indicated the contamination was confined to the new hospital building and not an issue at the adjacent Sir Charles Gairdner Hospital.

"We are confident that (flushing) will finish (the contamination), stop the problem, and we will be able to open the hospital. But we won't open until we have that and all other problems solved," he said.

Delays put pressure on Princess Margaret

The urgency to resolve the problem has intensified since John Holland failed to meet its last scheduled date for the completion and handover of the hospital building on November 30.

The Government had earlier pledged to open the hospital by the end of the year, but with the last missed completion date, conceded there were doubts whether it would be operating by the state election on March 11.

Dr Nahan says the hospital will not be opened until all problems have been resolved. ( ABC News: Andrew O'Connor )

The delays have put continuing pressure on Perth's existing children's hospital, the Princess Margaret Hospital, where staff have complained about lift failures and other maintenance issues.

Last week, Health Minister John Day acknowledged the possibility that lead-contaminated piping might have to be replaced if flushing did not clear the system.

But based on the latest advice, Dr Nahan said he does not believe that would be necessary.

"You might have to replace a few spots if it's caked in there, but that's it. There are four kilometres of piping in that hospital. We've gone through every inch of it," he said.

Dr Nahan said the additional costs associated with the delayed handover and commissioning of the hospital are "not huge" and would be dealt with through contract settlements with John Holland.

He said while not pre-empting John Holland's legal rights, he did not expect the matter to end up in court.

"I don't think it should. It's clearly their fault," he said.