Burst or leaking pipes wasted 30 billion litres of water - or 30 Patersons Stadiums filled to the goal posts - in the past twelve months, according to WA Auditor General Colin Murphy.
In his latest report tabled in parliament on Wednesday, Mr Murphy labelled the loss of water 'disappointing' and found that another 13 billion litres of water was also consumed but not billed, largely because of metering errors.
The Water Corporation supplied 357.39 billion litres of drinking water across Western Australia in 2012-13.
In his report, Mr Murphy said that while the network generally performed well, pipes are only replaced when they fail and ageing infrastructure is set to cause repair costs to soar from $9 million in 2010 to $40 million by 2019.
"While water loss cannot be completely eliminated from any network, it can be minimised, and it is disappointing that the Water Corporation is currently losing over 10 billion litres a year more than their benchmark," Mr Murphy said.
The Water Corporation uses a internationally accepted 'minimum loss' benchmark for leakages. In 2012-13 it was 10 billion litres above the benchmark. Between 7 and 8 billion litres of water is unaccounted for and thought to be from undetected leaking pipes.
"The Water Corporation is tackling water loss through its leak detection program and that has prevented an estimated 3.4 billion litres of leakage over the past three years," Mr Murphy said.
"Water Corporation currently does not consider undetected water leakage in prioritising pipe replacement. Bringing this into its approach would strengthen efforts to reduce water loss."
In response to the report, opposition water minister Dave Kelly criticised the Barnett Government slashing $350 million from the Water Corporation's maintenance program in the 2013-14 budget.
"It's very simple – if you cut $350 million from the Water Corporation's maintenance budget in an ageing system, it will cause huge amounts of water to be wasted," Mr Kelly said.
"This huge cut to water pipe maintenance will mean we will continue to see more water disasters like the ones that caused traffic chaos in the Perth CBD last year.
"New Water Minister Mia Davies must come out today and explain how she will prevent this extraordinary waste from continuing into the future and what she will do to re-instate at least some of the funding cut from the maintenance budget.
"This is an enormous amount of water to waste in a state where every drop is precious. The Water Corporation should be leading the charge in terms of water-saving measures in WA but this report shows it has lost all credibility."