A brief downpour on Wednesday flooded properties in Mary and Robjant streets, distressing residents who had just returned home or were still cleaning up after the February floods.

At a September meeting with Casey Council, a Melbourne Water spokesman told residents the area was not an "extreme" flood risk and there were no plans to update stormwater drains. New buildings were set above a one-in-100-year flood level, the spokesman said.

Residents said stormwater drains failed to cope with Wednesday's rain. They said they saw water coming out of the drains.

Robjant Street resident Trevor Goyal had raw sewage through his house from the February floods. He said that on Wednesday night it floated through his garage, where many of his possessions are stored while repairs continue.

Mr Goyal has suffered chronic health problems after cleaning up mould growing under the floorboards and behind skirting boards.

Ivan Grigson returned to his house in Karol Court, off Mary Street, on Thursday to find water inside and damp, muddy ground underneath.

He has been living off-site while his house dries out after the February floods.

"It's really set me back," he said. He now doesn't think his house will be ready to move back in until January, when the floorboards were scheduled to be replaced and repairs completed.

Clinical microbiologist Dr Cameron Jones told the Weekly that, from the photos he'd seen, many of the properties were affected by damp-related issues and sewage overflow. He said last week's flooding could not have come at a worse time as mould spores thrive in high humidity.

He warned that flood victims faced health risks from mould and damp homes.

"Anyone with pre-existing respiratory illnesses such as asthma is likely to become increasingly affected the longer they stay in these conditions."

Dr Jones advised people to immediately vacate damp or mouldy houses.