SA Water says it will not ramp up output from Adelaide's desalination plant, despite an extended dry period.

The state's reservoir levels are at 43 per cent of their 200-gigalitre capacity. This time last year, reserves were at 50 per cent.

Adelaide has seen just 17.8 millimetres of rain since New Year's Day, compared with an average of 108mm.

SA Water chief executive Roch Cheroux said the utility provider is waiting on winter rains to refill water stocks.

“We'll constantly monitor the state of consumption, match it with the weather forecast, and depending on that, we've got a number of options,” he said.

“But we're not planning to ramp up the desalination plant yet.”

Adelaide's desal plant has no trigger point for drawing water, which runs all year at a minimal level.

Mr Cheroux said the authorities would try pumping water from the River Murray into reservoirs if water stocks ran low.

“That's the second source of water we're using, and in case it's not sufficient, we can ramp up the desal.”

The State Government has warned irrigators that “extremely dry conditions across the Murray-Darling Basin” could see them open the season with just 14 per cent of their entitlements.