The South West's biggest water source, Wellington Dam, is overflowing for the second time in as many years but barely a drop can be used for drinking or industry at a time of dwindling rainfall.
The massive reservoir, which holds up to 185 billion litres or about half of Perth's annual needs, started overflowing this week, drawing tourists from around the region.
But after years of failed attempts to fix problems that make the dam's water too salty to use, questions emerged about how the resource could be allowed to go to waste.
Geoff Calder, the boss of irrigators' co-operative Harvey Water, said even though farmers were licensed to take up to 68 billion litres of water a year from the dam, they used barely half of the quota. He said this was because land clearing upstream had left the water too salty, meaning it was poor for irrigation and could not be sold to other users such as industry.
As evidence of this, industrial operators such as State-owned electricity utility Synergy had allocations of their own but invariably chose not to use them.
The Water Corporation, which has had to build expensive desalination and recycling plants in recent years to prop up Perth's drinking supplies, said it had not used the dam's water for years.
The utility had previously looked at options to take water from the dam but baulked at them because of high costs and the fact supplies were rainfall dependent.