Stormwater – helping to tackle Australia's water crisis
Box 1 | Australia's desalination situation
'Water, water everywhere, nor any drop to drink' – the famous line from Coleridge's The Rime of the Ancient Mariner could be describing the world's water situation. Only three percent of the Earth's water is fresh water, and two-thirds of that is locked up in glaciers and polar ice caps. Seawater accounts for the remaining 97 percent of the planet's water.
Australia is increasingly turning to desalination as a reliable additional water source that is independent of rainfall. Although desalination provides an almost limitless supply of drinking water from the ocean, the downsides of desalination are that it is expensive and requires a lot of electricity to run. Cities using desalination to boost their water supplies can expect significant increases in the cost of water. However, developing technology is bringing down the cost of desalination.
The desalination plants being built in Australia use reverse osmosis technology. In reverse osmosis, sea water is forced at high pressure through a semipermeable membrane, allowing fresh water through while retaining dissolved salts on the other side. It takes a lot of energy to force sea water through these membranes and hence desalination uses a lot of electricity – which in Australia is generated from fossil fuels. This is being addressed by using renewable energy to power new desalination plants. The Kwinana desalination plant in Perth is powered by energy from the Emu Downs wind farm, while Sydney Water plans to buy green energy from accredited suppliers to power the Kurnell desalination plant. The Victorian desalination plant will be capable of providing around a third of Melbourne's annual water supply using renewable energy sources. In South Australia, plans have been announced for the construction of Australia's first solar-powered desalination plant near Port Augusta to bolster water supplies perilously dependent on the Murray-Darling River system. The plant will be constructed within a complex that will also house a commercial salt production facility which will harvest the excess salt generated from the desalination process.
Desalination plants that discharge the concentrated salt water (or brine) are ideally sited where there are deep coastal waters and strong currents to disperse the discharge, which could otherwise affect coastal ecosystems.
Box
Box 2. Removal of pollutants from stormwater
Related sites
Desalination (Australian Water Association, Australia)
Solar-powered desalination plant leads the way (Ecos, No. 134, 2007)
Making water – hold the salt (Ecos, No. 124, 2005)
Posted June 2008.