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Canning Dam

  • Perth's winter rainfall below long-term average despite wet August
  • Rainfall runoff into Perth dams 81 per cent below long-term average
  • Water in Perth's dams mostly from desalinated seawater and groundwater, not rainfall

Despite Perth's wettest August in more than four years, winter rainfall across the metropolitan area was significantly below average in another stark reminder of the impact of climate change on traditional water sources.

Just over 395.4 millimetres of rainfall filled metro gauges from 1 June to 31 August - 16.5 per cent below the long-term (1876-2016) average of 473.7mm.

August rainfall (177.6mm) eclipsed the long-term average by 44.7mm, however, it was a dry start to winter with just 60.8mm falling in June against the long-term average of 173.1mm.

While any rainfall is beneficial, consistent rain is needed to soak dam catchments and for runoff, or streamflow, to be a reliable, year-round drinking water source.

Just over 64 billion litres of streamflow has been collected in metropolitan dams since January this year. The long-term (1911-1974) average to the same point in the year is 349 billion litres.

Prior to the mid-1970s, Perth averaged 420 billion litres of streamflow a year. Since that time, average annual rainfall has fallen by nearly 20 per cent, causing an 80 per cent reduction to streamflow. Today, 70 billion litres of streamflow is considered a good year.

To secure Perth's future drinking water in the face of climate change, the WA Government, through Water Corporation, has invested over $2.35 billion in climate-resilient water sources since 2001.

In 2022, the McGowan Government announced plans for a third multi-billion-dollar seawater desalination plant in Alkimos and commissioned a $320 million expansion of Perth's groundwater replenishment scheme - projects that will help ensure Western Australians continue to enjoy secure, sustainable drinking water long into the future.

Declining rainfall and the ever-increasing impacts of climate change on our precious water resources mean that being waterwise is now more important than ever. To learn more about the many ways we can all be waterwise in the home and garden, and how Perth's water supply is adapting to meet the challenge of climate change, visit

Comments attributed to Water Minister Dave Kelly:

"Even with decent falls throughout August, winter rainfall in Perth was still more than 16 per cent below the long-term average. This highlights the fact that it simply does not rain like it once did in southern parts of WA.   
"Instead of rainfall making up the bulk of our drinking water supply, around 85 per cent comes from desalination, groundwater and purified recycled water.

"While prudent investment in climate-resilient water sources has without question kept the taps running in Perth, we cannot underestimate the importance of staying waterwise. 

"Every drop of water saved means we can defer the need for expensive new water sources and help Perth become one of the world's most waterwise cities."