Campaigning for a fourth term in office, Howard released his water plan during a visit to Adelaide, capital of the arid state of South Australia.

"We waste an enormous amount of water in this country, we have to change our methods, we have to change our approach," Howard said.

"I can't think of a more important long-term conservation issue, it is the great conservation challenge of our time," he said.

"It is time to start securing Australia's water future."

Australia is widely considered to be the world's driest continent and large parts of the country have been beset by a long-running drought.

The proposed Australian Water Fund would focus on improving river flows, desalination of seawater for coastal areas, water recycling and developing water-efficient housing design.

"Through the Australian Water Fund, the coalition government will aim to achieve a cultural shift in water use and management to provide real benefits to all Australians," Howard said.

The conservative government has been strongly criticised by environmentalists for refusing to sign the Kyoto Protocol on curbing global warming.

The main opposition Labor Party has embraced the Kyoto treaty and built stronger ties to Australia's Greens party, which could determine the outcome of the October election.

The Greens' leader, Senator Bob Brown, said Howard's plan failed to address one of the single biggest problems -- the drying up of the Murray-Darling river system in the country's southeast.

"In today's statement, Prime Minister Howard has passed up the option for the government to do something memorable for the Murray River and the nation," he said.

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