The head of the Water Corporation has admitted many customers are using too much water, increasing the risk that the State Government may have to fast-track costly network expansion plans.
Corporation chief executive Sue Murphy told a parliamentary estimates hearing this week that efforts to reduce water use had not been as successful as intended.
After another dry autumn and amid predictions that Perth's winter rainfall will be below average, Mrs Murphy said the failure could have consequences for the corporation's future budgets.
She said reducing average water use directly affected the utility's ability to meet the Government imposed 2.5 per cent budget cut for public corporations.
It could also have ramifications for long-term spending plans because it would have to invest in multimillion-dollar expansions if demand was not reined in.
The comments were made as the Government's winter sprinkler ban came into force, with inspectors handing out dozens of warnings. The corporation said it would spare customers immediate $100 fines and instead issue warnings until Tuesday.
Shadow water minister Fran Logan said the Government should not have abolished Labor's rebate scheme for water-efficient appliances.
Water Minister Bill Marmion said though Perth dam levels were higher than this time last year, they were still at just 28 per cent of capacity.
He said the lack of storage and rainfall meant it was imperative people observed the sprinkler ban and reduced their usage.