The worst drought in a century, especially in Australia’s most populated and fastest growing regions, has forced state governments to make expensive, and in some quarters unpopular, decisions to secure water supply.As rainfall dwindles, new dams are a less-than-promising prospect, so governments have looked to the boundless resource surrounding the country — the sea — for an answer. Their solution: desalination.

Last year was Australia’s sixth warmest on record. It was the warmest in the Murray-Darling Basin and in South Australia, New South Wales (NSW) and Victoria. The south-west and south-east continue to suffer long-term low rainfall. The Australia Bureau of Meteorology, in its annual climate statement for 2007, reported that south-east Australia has now missed out on the equivalent of an average year’s rainfall in the past 11 years, making the current drought one of Australia’s most severe on record. The current drought is notable for its record high temperatures and record low inflows to water storages. The statement warns of a drying trend in the decades ahead.

Four states — Western Australia, Queensland, South Australia and NSW — either have working desalination plants or are planning to build them. Opponents say that producing the large amount of electricity required to run a desalination plant hastens climate change, which may be the culprit behind Australia’s drying trend.

Some governments have countered or appeased those arguments by building wind farms to offset the power needs of their desalination plants. In Queensland, Premier Anna Bligh has challenged energy companies to come up with the best way to power a planned desalination plant at Tugun on the Gold Coast using only renewable sources. She said recently: “I want industry to come to us with their best ideas — it could be solar or wind-generated power for example, it could be carbon offsetting, or it could be a combination. Making the plant carbon neutral will save 207,000 tonnes of greenhouse gas emissions every year — which is equivalent to emissions from 46,000 cars.”

Western Australia was first off the mark with a large-scale plant. Its Kwinana plant opened in November 2007. Now it provides about 45 gigalitres of water per year, about 17 per cent of Perth’ s needs. It is powered by a wind farm at Emu Downs, although the Australian Competition and Consumer Commission recently found that statements by the Perth Water Corporation that the plant was carbon neutral were misleading, and told it not to make similar claims in the future. The corporation is now calling for tenders for a new plant at Binningup, 155km south of Perth.

Victoria is building a plant at Wonthaggi in Gippsland which will supply about 150 billion litres a year, roughly one third of Melbourne’s water. The Victorian Government says it has already included the price of using renewable energy into the cost of the project.

Sydney’s desalination plant is being built at Kurnell on Botany Bay. The state government hopes to have it pumping 90 gigalitres of potable water per year from late 2009. To offset the power needs the state is building, with a private partner, a wind farm at Bungendore, east of Canberra. The 63-turbine farm is projected to have a capacity of 132 megawatts, about eight times greater than NSW’s existing installed and accredited wind power. Stung by public criticism of the plant’s power needs, the state government says that renewable energy certificates earned from the wind farm will provide clear public evidence that the desalination plant is powered by 100 per cent renewable energy.

The pioneer of desalination was South Australia, albeit small-scale. Since 1999 a plant at Penneshaw on Kangaroo Island has been providing with 300 kilolitres of fresh water every day. The island has no natural fresh water. In Coober Pedy, salty underground water is treated. At Marion Bay on the Yorke Peninsula a plant produces 60 kilolitres of water each day more cheaply than carting in fresh water. Now the state is going upscale, and has plans to build a plant at Port Stanvac that will initially supply a quarter of Adelaide’s water. The 50 gigalitre plant is expected to cost about $1.1 billion.

Desalination plants work by drawing in sea water and passing it through a porous membrane, which filters salt and impurities. The water is then treated with lime, chloride and fluoride to bring it up to drinking standard. Last, it is blended with fresh water from other catchment sources. What is left over, super-salty brine, is returned to the sea.

Not everyone is happy with desalination. Community groups have sprung up in each state where a plant is planned to oppose them on environmental and finance grounds. In South Australia, the Save Our Gulf Coalition says the planned plant at Port Stanvac presents many problems. Coalition chairman Peter Laffan says for one, the site is a contaminated former oil refinery. “Our chief concern is the brine in the Gulf St Vincent because it is very slow moving water and we have unusual phenomena in dodge tides; every two weeks there is no tidal movements for a day or so. That, together with the fact that flushing takes three to six months, means there is a significant threat that the brine will not disperse. Brine builds up in low-oxygen slugs that can create “dead” zones.”