In August 1996, a rare event drew 10,000 spectators to a major dam in Perth, Australia, as it overflowed after a wet winter. Fast forward to 2025, and despite experiencing significant rainfall, the Mundaring Weir is only half full. This situation raises questions about the water supply in Perth and highlights a broader issue affecting cities worldwide.

The climate in Western Australia has changed dramatically. Rainfall has decreased significantly, while summers have become hotter. The South West region, where Perth is located, has seen a 15-20 percent reduction in rainfall since the 1970s. Consequently, the amount of water flowing into Perth's dams has plummeted by 80 percent over the past 50 years. The annual streamflow has dropped from 420 billion liters to just 77 billion liters.

Evan Hambleton, general manager for asset planning and delivery at Perth's Water Corporation, expressed concern about the future of the dams. "We've had such a dry period for such a long time now, it's unlikely that we'll ever get back to where we saw significant inflows coming into the dams," he said. Although this winter brought some rain, previous seasons were dry, leaving overall totals still below historical averages.

The southern scarp, home to the largest dams, has experienced even less rainfall. The landscape has absorbed much of the rain before it can collect in the dams. "The catchments are like a big sponge," Hambleton explained. "It's only when that sponge is fully saturated that we start to see some run-off into streams then into our dams."

Previously, Perth required about 300mm of rain to generate run-off. Now, it takes approximately 500mm. The situation is exacerbated by increased evaporation from the dams and declining groundwater levels. Retired hydrogeologist Don McFarlane noted that groundwater has fallen by up to 10 meters, which previously helped maintain moisture in the valleys above the dams.

"There used to be the groundwater under all of these valleys … and they were keeping the valleys above the dams really wet," McFarlane said. He added that the recent winter rainfall was only slightly above average and insufficient to restore the region's water supply.

The decline in rainfall and streamflow in south-west Western Australia serves as a warning for other regions facing similar challenges. Areas like Iran, South Africa, California, and southern Europe are experiencing significant water stress. In Iran, water shortages have led to daily outages, while California is grappling with a severe megadrought.

Perth has turned to desalination to address its water supply issues, becoming the first Australian city to implement this technology in 2006. Today, desalination accounts for up to 40 percent of the city's drinking water. Hambleton acknowledged the importance of this technology, stating, "If we hadn't had desalination […] we would have had very severe restrictions in place."

The Western Australia government is exploring renewable energy options to power desalination plants, aiming for sustainability. Water Minister Don Punch mentioned, "We're looking at wind, solar and battery options in relation to the future energy needs of our desalination plants."

Despite the success of desalination, it has obscured the urgency of water conservation in Perth, which has one of the highest water usage rates in Australia. McFarlane suggested that innovative methods to increase groundwater supply should be explored further. He emphasized that while desalination has been beneficial, it should not be the primary source for non-essential water use.

Water Corporation has investigated various methods to boost streamflow, including thinning forests and cloud-seeding, but with limited success. As the population grows and demand increases, Hambleton stressed the need for efficient water use. "One of the things we know is that climate will continue to get drier not just in Perth, right across the South West … which means we need all customers to be more efficient in their use," he said.

Globally, regions facing similar challenges are implementing strict water conservation measures. For instance, Cape Town managed to reduce daily water usage by over 50 percent to avoid severe shortages. Australians have previously demonstrated their ability to conserve water during the Millennium Drought, and there is a renewed call for efficient water use in Perth. Hambleton noted, "On average, showers are taking much longer than the recommended four minutes."

As Perth navigates its water supply challenges, the situation serves as a reminder of the pressing need for sustainable water management in the face of climate change.