The role of dams in our modern water supply

In the South West corner of Western Australia, climate change is significantly affecting our water supply. Although your thoughts may wander to idyllic coastlines, lush forests and the spoils of nature’s pantry, Water Corporation faces the ongoing challenge of downward trending rainfall. Fun fact - If we received the same average rainfall as the 1960s, we'd have enough water to supply Perth's 2 million people. 

Less rain means less water is making its way into our dams, which in turn means we’ve had to adapt the way we supply water.

Will building more dams help collect more streamflow?

The problem is, contrary to popular belief, dams don’t act as bowls that catch rainwater.

When the sky opens up, rain first falls onto the natural landscape. The dam catchment areas soak up rainfall like a sponge. Only after the landscape is soaked does rainfall then flow into the dams which is called streamflow.

Due to less rainfall over the years, our catchment areas absorb most of the water. Our dams don't receive the volume of streamflow that they once did. And it doesn’t look like this will improve anytime soon, either. Winter and spring rainfall is projected to decrease around 15% by 2030.

So, even if we build more dams, there just wouldn’t be enough water flowing into them to make it worthwhile.

We've invested in rainfall independent water sources to secure our supply

As well as being one of our basic needs, water plays an intrinsic role in our WA lifestyles. It allows us to enjoy sports ovals, caravan parks, swimming lessons, green gardens and relaxing holidays. We rely on water in almost all aspects of our lives.

To continue to make new water memories, we have to reduce our vulnerability to changes in the climate. One of the primary ways we are able to do this is by diversifying to rainfall independent sources – seawater desalination, groundwater replenishment and water recycling.

Dams still have an important role to play in collecting available streamflow. However, these days they’re primarily used as storage reservoirs for our desalinated seawater and groundwater,  We store water during periods of low demand so it's available when we need it most, during the hot, dry summer months. Because of this our dam levels now go up and down independent of rainfall patterns. 

More information

IF you would like to know more about where your tap water comes from, check out Perth's water supply tool, Also, our 50-year water strategy has a cost comparison of water sources on page 29.