What is Groundwater?
When rain falls, some of it flows across the surface of the land and accumulates in rivers, lakes, and eventually the ocean. But some of the water seeps into the ground and accumulates within cracks or pores in the rocks (aquifers), forming groundwater resources, which in turn also eventually flow into rivers, lakes or the ocean.
Global water resources
Approximately 2 per cent of the Earth's water occurs as groundwater, compared with 0.1 per cent as rivers and lakes and 94 per cent as oceans.
In Australia, groundwater makes up approximately 17 per cent of accessible water resources and accounts for over 30 per cent of our total water consumption. Some groundwater is fresh and can be used for drinking. Other groundwater can be brackish water or even saltier than the sea. Some contain high levels of dissolved chemicals, rendering it unsuitable for human consumption or stock water supplies.
How is it extracted?
Depending on the permeability of the rocks containing the groundwater, and the pressure under which groundwater is held, the ease of groundwater extraction can vary significantly. Both water quality and aquifer yield determine whether groundwater is appropriate for human consumption, stock water supplies, irrigation, or mining uses. The salinity and yield characteristics of groundwater resources vary considerably across the continent.
Groundwater is particularly important as a water resource in semi-arid to arid parts of Australia, where rainfall is too infrequent or inadequate to reliably meet water needs. Often such groundwater resources have accumulated over long periods and are replenished only when rainfall is sufficient to infiltrate soil and rock. This means groundwater can be a finite, or slowly replenished resource.
In more temperate areas where rainfall rates are higher, groundwater may be replenished on a regular basis and extraction can be managed on a renewable basis. However, in many instances groundwater use in Australia exceeds the rate at which groundwater is replenished. For example, the Australian Water Resources 2005 concluded that 30 per cent of Australia's groundwater management units were at a high level of development and approaching or beyond sustainable extraction limits.