ABOUT WATER AND AUSTRALIA

Nothing has had a greater impact on Australia than water. Water has moulded its ancient landscape and influenced the pattern of human habitation from earliest times until the present. It will continue to influence people’s lifestyle, prosperity and their relationship with the land.

Australia is a continent of extremes: of geography, climate, population distribution and water resources. It is the driest inhabited continent on Earth, with highly variable rainfall patterns. This variability means that Australian communities frequently face water supply and water quality problems.

Scientists are now able to explain the reasons for these highly variable rainfall patterns and even to predict weather patterns across the continent.

Why is Australia's rainfall so variable?

The water sources available to any Australian community may include surface water - rainfall and the resulting runoff into streams and rivers - and groundwater - water from underground sources.

Only 12 per cent of the annual rainfall over Australia results in runoff into streams and rivers or soaks into and is retained in the ground. The rest is returned to the atmosphere directly by evaporation or from vegetation through the process of transpiration.

This results in Australia having only one per cent of the water carried by the world's rivers despite having five per cent of the world's land area.

The long term average annual rainfall over Australia is estimated to be 455 millimetres. However, this hides the very variable rainfall pattern across the continent.

Depending on seasonal conditions, Australians use enough water every year to fill Sydney Harbour almost 50 times – between 18 and 22 million megalitres of water a year. (A megalitre is one million litres - about the volume of an Olympic-sized swimming pool.)

According to the Australian Bureau of Statistics, 70 per cent of this water is used in agriculture for irrigation.

The most essential use of water is for drinking, but people drink only a tiny fraction of the water extracted from the environment.

The environment also needs water and, with most rivers dammed or regulated, this issue is receiving increasing attention from governments, communities and interest groups. Examples are the "cap" on the extraction of water from the rivers of the Murray Darling Basin, an area which includes inland regions of Queensland, New South Wales, Victoria and South Australia, and recent plans to restore the environmental health of the Snowy River in the east of Victoria.

To ensure a reliable water supply during periods of drought, large water storages have been built in Australia. In fact, Australia stores more water per head of population than anywhere else in the world. Examples of large water storages for urban use are:

• Warragamba Dam, supplying Sydney, which can hold about two million megalitres; and

• Thomson Dam, supplying Melbourne, which can hold about one million megalitres.

Water obtained from natural sources is not pure and because of conditions in catchments, variable rainfall patterns and other factors, the quality of water used in the water supply is likely to vary. Frequently it requires some form of physical and/or chemical treatment to make it safe and pleasant to drink.

Various technologies are used to remove contaminants from water and to improve and protect water quality.

Scientists, technologists and engineers with the Cooperative Research Centre for Water Quality and Treatment are developing new water treatment technologies and improving existing ones. Their work will improve water quality for many Australian communities and lower costs for Australian households and businesses.

One particular issue affecting water quality in many areas of Australia is the amount of salt dissolved in the water, called salinity. Salinity is now widely recognised as one of the nation's most devastating environmental problems. Federal, State and Territory governments are beginning to understand the full ramifications of the problem and are working with scientists and land managers to slow the rate of destruction and to repair the damage where this is possible.