From one extreme to the other - after floodwaters washed through several southern Queensland towns, they now face the prospect of no drinking water.

A deadly torrent of water raged down the Great Dividing Range at Toowoomba on Monday, crashing through several smaller towns in the Lockyer Valley below.

Many towns were either badly damaged or wiped out by the wall of water.

But the Lockyer Valley Regional Council now says drinking water has run out in the town of Withcott.

Helidon was also expected to run out of water overnight, with other towns, including Gatton, to follow in the coming days.

"It's becoming obvious now as the floodwaters go down, the extent of the damage and we are certainly going to have some problems," Lockyer Valley Mayor Steve Jones.

Laidley has about three days of drinking water left and residents are being told to use only what is essential.

Further west, residents of Chinchilla and Warra have been told to boil their water after an E Coli outbreak.

Toowoomba residents have also been told to boil their water as a precaution.

Fuel supplies are also running low in some areas and they are being restricted to emergency vehicles.

Even though the latest round of flooding has eased at Dalby and Chinchilla on the western Darling Downs, mayor Ray Brown says anyone wanting to buy petrol must apply to the local disaster coordination centre.

"We need to keep enough fuel for our emergency operations we know this is and inconvenience to people in our region we ask them to refrain from transport if they can to assist us with this," he said.