The drinking water at the problem-plagued Perth Children's Hospital is now safe, paving the way for the facility to finally open almost three years late.
Replacement of thermostatic mixing valve assembly boxes and brass fittings, which were leaching lead, was completed this month.
Tests conducted on 304 random water samples found lead levels were now below Australian drinking water guidelines.
Chief health officer Tarun Weeramanthri said 97.7 per cent had lead levels below the target of 0.01mg/L, exceeding the pass mark of 95 per cent.
"Compared to the figure of 74 per cent in June 2017, this indicates a dramatic improvement and effective remediation of the risk," he told reporters on Tuesday.
More than 300 staff are permanently on-site and have been drinking from bottled water.
Health Department director-general David Russell-Weisz said the lead issue had been "unprecedented and complex".
"We knew this was going to be a wicked problem," he said.
WA Health Minister Roger Cook said the public could now have every confidence in the $1.2 billion facility, but could not say how much delays had cost.
Opposition Leader Mike Nahan, who was criticised in a parliamentary report last week over his handling of the project while treasurer in the previous government, said it was a shame it had taken so long to resolve.
"I hope they have found the source of lead and resolved the myriad other problems that plague that hospital," he said.
"Let's be positive, we're finally getting access to one of the finest hospitals in the world for our children."
The hospital has had major construction problems including asbestos in ceiling panels and non-compliant fire doors.
Main contractor John Holland refused to agree to phosphate treatments to resolve the lead problem, which led to the government granting practical completion in April to take control of the site.
There is still a possible legal battle looming with John Holland.
A report tabled in parliament last week criticised responsibility for the project being divided between Strategic Projects and the Health Department.
A community open day will be held at the hospital on April 8 ahead of the official opening in mid-May.
Australian Associated Press
