It was one of a number of maintenance problems that came up at ACT Health annual report hearings on Friday.

Under questioning from opposition health spokeswoman Vicki Dunne, executive director of infrastructure management and maintenance Colm Mooney said theatre 14 at Canberra Hospital was shut down for a number of weeks June after mould was found.

"We found mould in an element in one of the Hepa filters which is a high efficiency particle air filter," he said.

Mr Mooney said maintenance worked with infection control to contain the mould and plan how the room would be put back into use.

Executive director of surgery and oral health Daniel Wood said the only other time theatres had to be shut down this year was when hydrologic works were done between March and June.

That was to upgrade pipes which have had issues with deterioration.

The Centenary Hospital for Women and Children  - which is on the Canberra Hospital campus - has had a litany of infrastructure issues, the hearing heard.

Extensive work has had to be done in the 15 delivery suits and bathrooms due water leaking into the wall cavities.

"Basically you've got soggy plasterboard and soggy vinyl floors," Mr Mooney said.

There have also been issues with the pediatric unit, part of which has been closed down for months due to plumbing issues.

Mr Mooney the issues were caused by a pin hole in a pipe, saying remediation works should be finished by Christmas.

The hearings also heard public patients were recently slugged for chemotherapy drugs despite the government promising to pay all co payments due to an "administrative issue”.

Canberra Health Services CEO Bernadette McDonald said everyone who had been improperly charged was written to last week with instructions to be refunded.

Mrs Dunne told the hearing she heard some staff with high amounts of annual leave banked up  had repeatedly - over a number of years - had their leave requests rejected.

Ms McDonald said she always encouraged staff to take their allocated leave every year.

Mental health minister Shane Rattenbury was pressed by opposition MLA Giulia Jones on the level of methadone prescription among prisoners at Alexander Maconochie Centre

She said some inmates had told her staff were prescribing methadone to prisoners to keep them "doped up" to keep them more subdued.

Mr Rattenbury said he was not aware of the practice and it was not one he would condone.

Executive director of mental health Katrina Bracher said she could not think of a health professional who would prescribe for that reason.

The government also defended the number of prisoners on a methadone program - which is significantly higher than most other jurisdictions.

Ms Bracher said the most recent figures showed 105 of just under 500 prisoners were on the methadone program.

She said it was an important health prevention method.

"We are a very progressive jurisdiction, we treat people's addiction based on a need not a cap system," Ms Bracher said.