Groundwater is water that is found below the earth's surface and is stored in the cracks and spaces in soil, sand and porous rocks. Most groundwater comes from rain that has infiltrated through the ground and has accumulated over many thousands of years. The study of the distribution, movement and quality of groundwater is known as hydrogeology.
Soil, sand and rocks that are able to store and transmit useable quantities of groundwater are known as aquifers. Aquifers that are closest to the ground surface are called shallow or unconfined aquifers (their upper surface is the water table). There are also deeper, confined (sometimes called artesian) aquifers where the water is confined under pressure between impervious layers, like clay. These aquifers can be hundreds of metres thick.
Groundwater is a critically important resource in Western Australia and we rely on it to prosper and grow and in some areas of the state it is the sole supply to many towns. In Perth we are lucky because the city is built on a multi-layered aquifer system commonly called the Gnangara groundwater system. The aquifers of the Gnangara groundwater system are part of a sedimentary basin called the Perth Basin.
Other parts of the state also contain vast quantities of groundwater , which is stored in other sedimentary basins: the most important ones we use are the Carnarvon and Canning basins. Smaller groundwater resources can also be found in fractured rock aquifers, as well as in old, buried riverbeds, called paleochannels. There are important paleochannel aquifers found throughout much of the arid zone of Western Australia, where they are often the only reliable source of water.