Western Australia's worst water guzzlers will be hit with an up to 16 per cent jump in their water bills.
The state Labor government's new efficiency pricing mode will mean water-wise households will see an average bill increase of 5.5 per cent.
Premier Mark McGowan said it was the "fairest" option possible to lower a planned price-increase for average households and put off the need for another $1 billion desalination plant.
"The longer you can put off building one the better it is for taxpayers," he said.
Water Minister Dave Kelly said the model incentivises the state's worst water guzzlers to be more waterwise, "which is important as climate change continues to severely impact our rainfall levels".
The forecast increase for average households is lower than the original six per cent rise under the old pricing model.
But guzzlers in Perth who use more than 500KL will be slugged an average 16 per cent increase, while regional wasters will be hit with a 10 per cent jump.
In total, WA's worst water guzzlers make up less than seven per cent of Perth households but use 17 per cent of Perth's residential water use, according to the government.
"The Water Corporation will write to households who used more than 500KL last year prior to the implementation of these changes on July 1, 2018," Mr Kelly said.
"This will give those impacted households the opportunity to moderate their water usage."
To soften the blow of the price hike, the government announced on Wednesday three new schemes to help people pay their water bills, including a hardship debt program and assistance for people with kidney disease who need large amounts of water for home dialysis.
Costing about $100,000 per year, the funding will be set aside in this week's state budget.