Water supply

Western Australia's water supply is currently sourced from groundwater, groundwater replenishment, desalination and our dams (surface water).

The use of these water sources currently differs from town to town across WA, depending on the location and climate conditions of that area.

Perth's water supply

Perth's water supply consists of water from all 4 main sources. With the largest population in WA, and a steady decline in average rainfall, it is important to diversify our water sources to ensure there is enough water for everybody.

Regional Western Australia

Regional water supply consists mostly of groundwater and dam water with a small amount of desalination used in some areas. Depending on location, size and climate, different towns and cities will source their water from different places.

Our sources

Desalination is the process of removing salt from sea water to produce water that is for drinking or for use by industries which require very pure water. Desalination provides a reliable water supply to cities and towns with minimal rainfall that are located close to the ocean, such as Perth.

There are currently two desalination plants located in Western Australia in Kwinana and Binningup

Sourcing the water

The first stage in the desalination process is drawing water out of the ocean through the use of a seawater intake.

Treatment

  • Screening: During this process, any large objects that have entered the plant from the seawater intake are removed.
  • Dual media filter: This process helps to remove any solid materials from the screening process.
  • Reverse osmosis: This step places water under pressure as it passes through tubes containing tightly wound membranes and tiny pores. Water molecules are forced through the membrane, leaving dissolved materials behind.
  • Energy recovery: The energy recovery units help to recapture and feed back into the system most of the energy that is used during the treatment process.
  • Diffuser: Salt that was removed from the water during the reverse osmosis process is then mixed with some of the purified water, and dispersed back out into the ocean.
  • Mineralisation: The fresh water is then diverted to a mineralisaton tank where chlorine is added to disinfect and clean the water, as well as flouride to help prevent tooth decay.
  • Storage tank: The water that has been through the mineralisation process is then pumped to a storage tank which is then later added to the water supply.

The desalination process

Groundwater is water located in the space between soil and rock beneath the Earth’s surface and is an important part of water supply in Perth and Western Australia.

Storage

Groundwater is stored in aquifers which consist of underground layers of rock or sand that can absorb and hold water. 

The water stored in these aquifers can be made up of rainwater that has filtered through the Earth's surface into the aquifer, or of recycled water which has been pumped back into the aquifer through the process of groundwater replenishment.

The ability of the water to move freely underground depends on the type of rock and whether the aquifer is unconfined or confined. In Perth there are three layers of aquifers:

  • Superficial aquifer: The shallowest aquifer which stretches across the coastal plain and includes the Gnangara Mound. Superficial aquifers are located closer to the surface and often appear as wetlands or lakes. They are the main groundwater source for home garden bores, and bores used for schools, parks and playing fields.
  • Leederville aquifer: Sits below the Superficial aquifer, and is generally separated by dense layers of materials, such as clay and shale, that minimises water movement between aquifers. The Leederville aquifer is up to several hundred metres thick, and in some areas it connects with the surface.
  • Yarragadee aquifer: The oldest aquifer that extends from Geraldton in the north to Albany in the south and has a limited connection to the surface environment. It provides a stable supply of water, even in dry years, because of its vast storage capacity.

Extraction

Groundwater is extracted from the aquifers with the use of bores. Bores can be used on a small scale by households, local councils and businesses to water gardens, lawns, parks and ovals or on a larger scale to extract water for a town or city'swater supply

Treatment

Before the groundwater is safe to drink, it has to undergo 4 different stages of treatment:

  • Aeration: the process of removing any trapped gasses and adding oxygen by spraying the water into the air.
  • Clarification: the removal of any sediment in the water
  • Filtration: the filtering stage which removes any leftover particles that remain once clarification has occurred
  • Mineralisation: the process of adding chlorine to disinfect the water and fluoride to protect against teeth decay.

Once the water has been treated it is then pumped through a network of pipes, pumps and reservoirs into the water supply.

Dams are storage reservoirs constructed to help collect and hold surface water. They are built in rivers and have traditionally provided the majority of water for many towns and cities in Western Australia, particularly in Perth. While dams in the north west of Western Australia continue to receive enough rainfall to supply connecting towns, a shortage of rainfall in the south west has meant that dams in the area are increasingly being used to store and move desalinated water and groundwater around the system.

Capture and storage

The way water is captured and stored changes depending on the type of dam. Currently in Western Australia we use 4 different types of dams:

  • Main dams: a major reservoir in a valley which supplies water directly to users 
  • Pipeheads: a small dam that has been diverted from a river that stores water and supplies directly to users  
  • Pumpbacks: similar to a pipehead, pumpbacks divert water from a river and then pump water to storage reservoirs 
  • Diversion dams: a dam that diverts a river straight into an irrigation system for use on crops and farmland

Treatment

Water from dams that is used for drinking water purposes has to be filtered before it will undergo a process called mineralisation. During mineralisation, chlorine is added to the water to disinfect and clean the water, as well as fluoride to help prevent tooth decay.

Once the water has been treated it is then pumped through a network of pipes, pumps and reservoirs into the water supply.
 

Canning Dam

 

Groundwater replenishment treats wastewater to drinking water standards before recharging it back into our groundwater supply.

The water is then stored in the ground until it is extracted some time later, treated further and supplied to Perth’s drinking water system.

How is water treated for groundwater replenishment?

Before entering the Advanced Water Recycling Plant, the wastewater has already undergone rigorous treatment at a wastewater treatment plant, including the removal of most chemicals and nutrients, detergents and heavy metals.

It then undergoes further treatment to remove any trace levels of micro-organisms and chemicals to meet drinking water standards.

Treatment

  • Ultrafiltration: This step separates out all the molecules from the water that are larger than 0.1 of a micron, which is equivalent to 1/300th of a human hair.
  • Reverse Osmosis: This step places water under presure as it passes through tubes containing tightly wound membranes with tiny pores, 100 times smaller than ultrafiltration. Water molecules are forced through the membrane, leaving other dissolved materials behind.
  • Ultraviolet disinfection: The water is subjected to ultraviolet light as a final disinfection step to destroy any trace levels of micro-organisms that may remain.

Throughout the treatment process, the water is continuously monitored to ensure strict water quality guidelines are met.

After this process, the recycled water is now of drinking water quality. It’s then recharged into an aquifer where it mixes with the existing groundwater. This recharge amount is less than 0.1% of their total storage, so it’s only a drop in the aquifer. Over time, we won’t be able to tell the difference between the recycled and existing groundwater.

Test your knowledge with our water supply e-learning games!

Water sources

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Water supply - upper primary school 

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Water supply - high school

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