Australia's water resources are highly variable, and range from heavily regulated working rivers and groundwater resources, through to rivers and aquifers in almost pristine condition.
Rainfall in Australia is highly variable from year to year, and season to season. On average, only a tenth of this rainfall becomes runoff into rivers or recharge into groundwater aquifers. We rely on groundwater to meet our water needs where surface water is unavailable. Groundwater makes up nearly one-fifth of Australia's 'sustainable' water resources.
Australians live on the driest inhabited continent in the world. Rainfall is variable and droughts are common, and water resources in many areas are scarce. Where surface water is unavailable, we rely on groundwater to meet our water needs.
Rainfall in Australia is highly variable from year to year, and season to season. Average rainfall across Australia ranges from less than 200 mm per year in central Australia, to more than 2000 mm per year in some coastal areas in the far north and far south.
The most recent water figures from the Australian Bureau of Statistics show that in 2008-09, rainfall for Australia was 519 mm. Compared to 2004-05 and average levels of rainfall, 2008-09 was a wet year. However, below average rainfall and drought was experienced throughout much of Australia in 2008-09, specifically south eastern Australia.
In the 12 months from September 2008 to August 2009, highly populated areas in New South Wales and Victoria, including the Murray-Darling Basin were under stress, with below average rainfall. The south-east of Australia has been abnormally dry, while the north-east has been abnormally wet.
On average, 90% of rainfall is directly evaporated back to the atmosphere or used by plants; only 10% becomes runoff into rivers or recharge into groundwater aquifers. This runoff and recharge is highly variable, resulting in significant differences in water availability across Australia.
In 2004-05, total runoff was estimated at 242,800 gigalitres and total groundwater recharge at 49,200 gigalitres. This gives a total inflow to Australia's surface and groundwater resources of 292,000 gigalitres (10% of rainfall). Based on these figures, runoff to rivers made up 83% of total inflows, and groundwater recharge accounted for 17%.
Runoff is not evenly distributed across the country. In 2004-05, more than 60% of Australia's total runoff was in Australia's three northern drainage divisions:
- Gulf of Carpentaria drainage division (62,060 gigalitres)
- Timor Sea drainage division (50,240 gigalitres)
- North-East Coast drainage division (40,210 gigalitres).
In contrast the Murray-Darling Basin was relatively dry, accounting for only 6% of Australia's runoff in 2004-05.
There are 501 large dams in Australia. In 2004-05 the total storage capacity of these dams was 83,853 gigalitres.
- Information on current dam levels across Australia is available from the Bureau of Meteorology
In addition to large dams, there are more than two million farm dams across Australia. These dams are estimated to have a total storage capacity of 8000 gigalitres.
Groundwater makes up approximately 17% of Australia's 'sustainable' water resources. Much of Australia's groundwater is drawn from the Great Artesian Basin - the largest groundwater reserve of its type in the world. It covers 22% of the Australian continent and contains water that is up to two million years old.
Determining how much groundwater is available is difficult. Compared to surface water systems, we know little about groundwater systems, and in many areas across Australia, surface water and groundwater resources are physically connected (for example a lake might recharge a groundwater system, or groundwater might keep a river flowing when it is not raining).
The most recent water report from the Australian Bureau of Statistics shows that 380 gigalitres of groundwater was extracted from the environment by the water supply industry in 2008-09, while 8956 gigalitres of surface water was used.
Of the total 1,779 gigalitres of water discharged by the industry in 2008-09, about 65% was discharged to the sea, 34% to inland surface water and 1% to groundwater.