It will be the first time in nine years that limits on water use are imposed on the city of four million and surrounding areas and comes despite recent rains that promised an end to the country's worst dry spell on record.

The restrictions, to take effect October 1, ban the use of sprinklers and watering systems and the hosing of all "hard surfaces", including vehicles. Violators will be fined 220 dollars (145 US) per incident.

The crackdown was announced by New South Wales state Premier Bob Carr during a visit to a water reservoir oustide Sydney.

"The reason we're doing this is that the dam levels behind me are way lower than they should be at this time of year," Carr said.

Carr said the restrictions had been decided because of concerns that the past year's drought combined with excessive water use by Sydney residents would drive reservoir water levels to danger levels in the upcoming southern summer.

Dam levels within the Sydney Catchment Authority are currently at 60.5 percent of capacity, still above the 55 percent level when mandatory restrictions are normally applied.

But Carr said with the start of warmer weather it was responsible to introduce the restrictions now.

"Basically there's three rules from now on," state Energy Minister Frank Sartor said.

"If you want to water your garden, use a hose; if you want to clean your footpath, use a broom; if you want to wash your car, use a bucket."

The restrictions will remain in force until water storage levels reach 70 per cent, he said.

Carr said global warming was in part to blame for the problem as rainfall had been lower than average in the region for nine years, while average temperatures are climbing.

"Those people that are sceptical about global warming ought to think again," he said.

SPACE.WIRE