There were multiple opportunities for asbestos to be identified during work on the Minnivale Reservoir, but contractors were uninformed, Western Australia's Water Corporation has found.
A total of 138 people visited or worked on the refurbishment of the Minnivale Reservoir, about 180km north-east of Perth, between March and September.
An investigation into the exposure of employees and contractors also established that the asbestos-containing material removed from the site was contained either at a landfill facility or on-site.
Extensive sampling of the Minnivale Reservoir site did not identify any asbestos fibres, the Water Corporation said.
An independent expert in asbestos risk management also conducted a re-enactment of grinding work undertaken at the reservoir and found that asbestos was not present at a concentration exceeding the workplace exposure standard set by the National Occupational Health and Safety Commission.
Water Corporation chief executive Sue Murphy said she was sorry for the concern caused to employees and contractors.
"I want to assure not only these people, but also the West Australian public, we are taking full responsibility in every respect," she said.
"An analysis of about 1000 projects carried out in recent years shows no other such failure to communicate the risk of asbestos but we are taking all necessary steps to prevent this situation from ever occurring again."
Ms Murphy said the Corporation's governance, processes and accountabilities for asbestos management had been reviewed.
But the Community and Public Sector Union/Civil Service Association says the government "took its eye off the ball" and unnecessarily exposed people to asbestos.
Assistant secretary Rikki Hendon said the incident occurred because the Water Corporation was too busy cutting back its workforce at the request of the state government while the project was taking place.
"This is about the most serious process failure you can have where people's safety and well-being is compromised," she said.
Opposition spokesman for water, Dave Kelly, has called for an independent inquiry into the incident.
