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.
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.
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.
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.