Role of dams evaporates fast

Although he might not have known it at the time, Jens Jorgensen showed remarkable prescience on a wintry afternoon in 1996.

It was Tuesday, September 9, and while the overflowing Mundaring Weir had whipped up a storm of excitement, the local publican suspected it was an event not to be repeated.

More than 15 years later, his suspicions have proved prophetic.

Despite the vagaries of stream flows and dam levels along Perth's Darling Escarpment, the relevance of Mundaring and the city's other dams has been in a steady decline ever since.

Last year, after the second driest winter to hit Perth and record low dam inflows, water levels at the Mundaring dam are sitting at 37 per cent and falling.

Predictions by the Water Corporation suggest dams like Mundaring might become nothing more than a storage facility for the desalinated and recycled water.

The once dominant role of dams in providing Perth and the South West's drinking water is evaporating as fast as the water within their walls.

This is the defining nature of the State's water conundrum - where are we going to get our drinking water from in a drying climate?

Since the 1970s, Perth has been receiving about 13 per cent less rainfall than the historic average but far less water has been running into its dams or seeping into its aquifers.

Water Corporation chief Sue Murphy admits it is a concern, but dismisses any notion that Perth could run out of water.

She said there were three key ways to secure water supplies over the next 10 years: developing new water sources, particularly desalination plants, increasing the amount of recycled water including aquifer recharge, and reining in per capita use.

Evidence of WA's increasing enthusiasm for desalination plants is obvious.

The Kwinana desalination plant, the first major facility of its kind in Australia, has been pumping 45 billion litres a year into Perth's drinking supplies since it was commissioned in 2007.

The State's second plant at Binningup is due to come on stream this year.

While desalinated seawater and other promising technologies, including a plan to pump up to 35 billion litres of treated sewage into Perth's groundwater offer hope, they have downsides.

Water economist Phil Pickering notes these options are expensive and inevitably entail higher household water costs. Mr Pickering said they had much higher treatment costs than either dam water or groundwater and this meant tariffs would rise over the next decade.

Not surprisingly, both Mr Pickering and Ms Murphy say reduced consumption is the most sensible way to shore up water supplies.

In Perth, household consumption rates are among the highest in the world despite the city's position at the pointy edge of climate change and a rapidly growing population.

University of WA visiting professor of environmental engineering Paul Hardisty said the price of water needed to be set at its full cost and it would continue to be taken for granted until this happened.