A potable water shortage is now the main problem faced by residents at Brisbane after brown, muddy floodwater seeped into the city's largest treatment plant.

This, as the Insurance Australia Group on Wednesday said that damages cost by the floods of ex-tropical cyclone Oswald that streamed into the ocean from rivers near Rockhampton, Bundaberg, Maryborough and Gladstone now stand at $200 million, and could still rise in the coming days.

Brisbane residents have been advised that although the Mount Crosby Water Treatment Plant is partially online, they ought to conserve water and use it only for drinking, showering, cooking and cleaning.

"I want people to be assured what water they are receiving is tested and is healthy," Graham Quirk, Brisbane Lord Mayor, said.

However, water at some some suburbs could run out, of which most at risk are Tarragindi, Camp Hill, Carina North, Mt Gravatt, Tingalpa, Rocklea and Oxley.

"They all have small reservoirs that feed those particular suburbs and they would be the first to be hit."

Stocks of bottled water have been prepared just in case clean water does run dry today.

"If any reservoir runs dry, we'll be immediately providing that for distribution to local areas," Premier Campbell Newman told ABC television. "This is very serious."

Insurance Claims

Flood-related claims linked to ex-tropical cyclone Oswald have now reached 6,500 cases, with the latest 4,500 filed from victims in NSW and Queensland in the past 24 hours alone, according to Insurance Australia Group.

Damages from the destruction have been estimated to have reached more than $130 million, IAG said. Its reinsurance program, the company noted, is only up to $150 million.

Lesson Still Not Learned

Despite the number of claims, however, they are those in Queensland who still haven't inked flood insurance.

A survey by the Industry Advisory Group in June 2012 revealed 40 per cent of Queensland homes remain uninsured against floods, despite the state's first disasterous flooding experience in 2010-11.

Alex Lo, Griffith University environmental economics lecturer, said many of the residents thought what happened in the summer of 2010-11 would not occur so soon.

''They think it is a one-in-100-year flood, so they think it is not going to happen at least in the next 100 years,'' he said.

Suffice to say, history this week has proven them wrong.

Read more:

Queensland Gets Flooded, 20 Rescued

Mother and Her Four Children Trapped on Roof at Queensland Due to Cyclone Oswald Floods, Rescued