The low-risk bacteria was found in hot water systems in the building's Senate wing as DPS staff were conducting water testing as part of a building safety assessment.

A spokesperson said one water sample indicated the presence of a strain of Legionella, but there was no indication of the potentially deadly Legionella pneumophila bacteria that can cause Legionnaires' disease.

An internal email to staff in the building said Legionnaires' disease could only be contracted by inhalation and not ingestion.

Urgent maintenance works have been planned for the Senate wing on Friday evening and hot water systems will be flushed with high temperature water to address the problem.

"To ensure we comprehensively address the issue, it is necessary for DPS to flush each hot water outlet for a period of time with water that is at a higher than usual temperature," the email said.

"The water temperature will begin to rise from midday today in preparation for the maintenance work that will commence at 5pm. DPS maintenance will undertake the work, escorted by parliamentary security officers."

"DPS has received expert advice that the proposed approach is appropriate to address the issue."

Press Gallery president David Speers warned journalists working at Parliament House to be careful of the increased water temperatures from taps.

He said press gallery offices could be accessed after 5pm as the flushing continues.

Most MPs and senators are away from Parliament House this week, with sittings not scheduled to resume until September 22.

Prime Minister Tony Abbott is in Melbourne on Friday.

The 4,700 room building and 32-hectare site hosts thousands of public servants, journalists and other staff, with the working population increasing significantly during sitting periods.