South East Queensland's largest dam has fallen below 50 per cent, its lowest level in a decade.

The region's combined dam levels are at 61 per cent and without decent summer rain, the region could be on water restrictions by the middle of next year.

The Gold Coast de-salination plant usually provides about 20 per cent of the region's water supply, but that will be ramped up to a third over summer, the most it's ever been relied upon.

Wivenhoe Dam (Dean Saffron)

The plant was built during the Millenium drought, when levels dropped to 20 per cent.

Mandatory water restrictions will be introduced when combined dam levels drop to 50 per cent.

"If we can start to bring that water use down it will certainly help delay the need for restrictions and potentially avoid them," Mike Foster from SEQ Water said.

But the levels won't impact house-hold water bills until next year at the earliest, as water prices are fixed at three-year intervals.

Water minister Anthony Lynham has urged Queensland's to heed the warnings and not waste water.