In 2007, Perth all but secured its drinking water supply for the future thanks to early investments in technologies like seawater desalination.
But trickling away in the background is a serious water problem the city is yet to solve.
- Perth has a growing groundwater problem
- The decline is threatening wetlands and vital non-drinking water supplies
- Experts say the government needs to look harder at water reuse options
Perth’s number one water source – groundwater – is drying up.
It is a chronic problem threatening the city’s vital non-drinking water supplies and groundwater-reliant ecosystems.
But as the state government looks at a further cut of 19 per cent to water allocations, there are fears it will fuel heat islands in suburbs as public parks, ovals and private lawns dry up and die.
Some experts argue there are other solutions that are not being driven hard enough.
This includes reusing some of the hundreds of billions of liters of water pumped from wastewater treatment plants and drained from urban areas into the ocean and inland waterways every year.
Wetlands a window into superficial aquifer
Looking over the muddy and shallow remnants of Perry Lakes, a once thriving wetland, the problem is becoming increasingly visible to the assistant professor of hydrogeology, Don McFarlane.
“In previous years this lake system would have been full to overflowing, you never get that now,” he said.
“You can see peat being exposed on the bottom.”
He describes wetlands as a window into Perth’s superficial aquifer, an underground layer of rock where groundwater is stored, but the state of many of them paints a dire picture.
Data from the Department of Water and Environment Regulation (DWER) shows while water levels in some areas are stable and others are rising due to urbanization, many are in decline.
“I think one of the great things about Perth is we’ve adapted enormously quickly to the drinking water problem by adopting seawater desalination and doing groundwater replenishment,” he said.
“But the attention now needs to be on securing non-drinking water supplies, particularly water from the superficial aquifer under Perth.”
Perth’s Gnangara groundwater system is made up of three aquifers.
There are the large and deep Leederville and Yarragadee aquifers, which the Water Corporation mainly draws from for drinking water.
And then there is the shallow, unconfined superficial aquifer, which is what fills the wetlands and is used for non-drinking water supplies such as irrigation, domestic gardens and ovals.
A combination of climate change and water abstraction has led to 1,000 gigalitres of groundwater being lost from the superficial aquifer since 1980, according to DWER.
Water extraction cuts on the table
The loss of water from the superficial aquifer is a problem the state government is working hard to solve.
It released a detailed document called the Gnangara Groundwater Allocation Plan for which a four-month consultation period has just ended.
If implemented, the plan will see home bore users have their sprinkler days reduced from three to two per week.
It would also see the allocations for license holders, such as local governments and industry, reduced by 10 per cent, and the Water Corporation’s abstraction be reduced by 27 per cent.
WA Minister for Water Dave Kelly said the cuts were necessary to maintain Perth’s green spaces and minimizing the urban heat island.
“I know some people won’t be happy about [the plan] but by and large people understand the days of using our water, regardless of being precious, have really changed. “
‘Sleepwalking into a browser, hotter and drier’ future
But Dr McFarlane, and other water experts, are questioning whether it is the best and only solution.
Dr McFarlane said the government was leaning too heavily on pumping reductions to solve the problem.
“My concern is that Perth would be slowly sleepingwalking into a browser, hotter and drier urban environment,” he said.
“I think we underestimate how much the evaporation from lawns and gardens is actually contributing to keeping Perth a relatively cool city.”
He said there were localized options to recharge the aquifer that weren’t being driven hard enough.
This included diverting some of the water from main drains, and ramping up wastewater reuse for irrigation.
“That’s about twice the proposed cut in extraction.
“Not all of that water can be diverted into the aquifer but there are a lot of opportunities where that could occur.”
He said in addition to that, 110 gigaliters of highly treated wastewater was pumped into the ocean every year.
“There’s evidence from Mandurah, Kwinana and rural areas that we can safely infiltrate some of that water to raise groundwater levels around wetlands and later use it for irrigation which will help cool Perth.”
In the Town of Cambridge, a project is underway to divert excess water from the Herdsman Main Drain to Perry Lakes to raise lake water levels.
The state government is funding part of the project.
Dr McFarlane said if those kinds of projects became common practice, as was the case in rural and regional areas, the benefits would add up.
“The government is starting to do this in a few areas, but there’s no sense of urgency,” he said.
He said local governments often lacked the experience and resources to do water reuse by themselves.
“The state government, Water Corporation and local government need to work together and not just share knowledge and resources, but also share risks because we all benefit from having healthy communities.”
Fear of dry suburbs
For Marmion resident Lahnie Davies, who shares a bore between 18 homes on the street, the sprinkler cuts feel like an unfair penalty, and one that may not even work.
“I think what it will do is push people onto town supply, they will start watering with their hose, and that defeats the purpose,” she said.
Their bore was installed at a cost of $ 35,000, at a time when the government was encouraging people to switch to bore to take the pressure off the drinking supply.
She said they would not be able to maintain their lawns and gardens on a two day a week sprinkler roster.
“We’ve gone to great lengths to plant plants that are water wise and we just won’t survive even on two days a week,” she said.
Costs a factor in proposal
The Water Minister said the government was looking at local reuse options.
But he said costs needed to be considered.
“Asking water users to be more efficient with the water we already have is the cheapest way we can save water,” he said.
“We are looking at local options to assist our wetlands, all those possibilities are there.
Mr Kelly said there had been sprinkler roster changes previously, and time had shown green private gardens could still be achieved.
However, he said the plan was not set in stone and a final decision would be made once submissions from the consultation period had been examined.
Whatever the solution, one thing most water experts agree on is that if Perth’s groundwater is to be preserved, something will need to change.