One-off rebates on South Australian water bills have come into effect today after the State Government increased water prices last year to pay for the desalination plant.

Households using more than 120,000 litres will have $75 deducted from their next bill while consumers using less than 120,000 litres will be entitled to a $45 reduction.

The rebate was announced before last year's state budget to offset part of the cost of a 25 per cent water price rise in July.

Attorney General John Rau says the Government will spend $45.7 million on the rebates to about 600,000 customers.

Mr Rau says sudden price hikes like the one in July will no longer occur.

"Water rate increases, if any, will be occurring perhaps on CPI basis or whatever it is over the years to come, but there won't be these big jumps that there have been," he said.

"This rebate is intended to recognise and help people deal with the fact that there have been jumps in overall water costs."

The rebate will be based on last year's water consumption figures and will be deducted from the first household water bill of 2013.