Teacher background information
What is groundwater?
Groundwater is water that occupies the spaces between particles of soil (sand, silt and clay) or rock beneath the earth’s surface. The source of groundwater is rain, which infiltrates the soil. Groundwater moves quickly through sandy soils where it reaches the water table. As a result, large volumes of groundwater can often be pumped from wells (bores) sunk in sandy soils. Limestone is more porous than granite and holds more groundwater. Groundwater is found in unconfined (shallow) aquifers and confined (artesian) aquifers. Unconfined groundwater occurs near the land surface and receives direct rainfall recharge. Confined groundwater occurs beneath a layer of impervious material and may be under pressure.
The water table
The top surface of unconfined (shallow aquifer) groundwater is called the water table. The water table is usually below the ground surface. However, when the water table is high enough, groundwater comes to the surface naturally in springs, lakes and ponds (wetlands). The level of the water table may fluctuate, rising in winter after rainfall has recharged the aquifer, and falling during periods of low rainfall, when the volume of groundwater pumped increases or is drawn upon by vegetation.
Perth’s groundwater supply
Perth’s groundwater comes from artesian bores and two major groundwater mounds: the Gnangara Mound in the North and the Jandakot Mound in the South. This water is treated by Water Corporation at the following treatment plants prior to distribution to consumers: Wanneroo, Mirrabooka, Gwelup, Jandakot and Lexia. In addition to public water supply, privately owned bores in the Perth urban area draw another large groundwater supply. Groundwater pumped from these bores is used for irrigating domestic gardens, market gardens and public open space.