Groundwater and its use in Perth

The largest source of water for the Perth Metropolitan Area is north of the Swan River, right beneath our feet.

Rainfall seeps through our soils and becomes part of the Gnangara groundwater system.

Because we are now getting less rain, how much water we use and how much goes back into the groundwater system has become a major concern for everyone who lives in Perth.

The groundwater stored in the Gnangara system provides the people of Perth with 60 per cent of their scheme water needs. Most of this water is mixed with water from other sources such as dams, and then treated and delivered to our homes.

Large volumes of water from the Gnangara system are also used for agriculture, forestry and market gardens, and by local government authorities and private bore users. It is also an important source for maintaining our precious wetlands and native vegetation.

What is the Gnangara Mound and system?

The Gnangara Mound is the name given to the sandy watertable on the Swan Coastal Plain north of the Swan River. It is so named because the landform literally forms a mound across this area.

At its highest point the mound is about 70 metres above sea level and slopes away in all directions—east to Ellen Brook, south to the Swan River, west to the Indian Ocean and north to Gingin Brook.

The sandy watertable is known as the 'superficial' aquifer. On the crest of the mound there is fresh groundwater up to 60 metres deep.

Underneath the superficial aquifer are two other geological formations, the Leederville (500 metres deep) and Yarragadee (1000 metres deep) aquifers. These are known as 'confined' aquifers because their waters are contained within layers of rock.

There also a number of smaller aquifers such as the Mirrabooka and the Kings Park aquifer.

The confined aquifers and the superficial aquifer make up the Gnangara groundwater system.