On the cracked grey clay of an ancient lake bed on the edge of Australia's outback, Guy Kingwill is at the frontier of a global rush to commercialise water.

Despite a long-running drought, Mr Kingwill, who runs the vast Tandou farm, 142kms southeast of the mining town of Broken Hill, has just sold his property's critical water on a national market rather than pump it into irrigated cereal crops.

"The return on the water is higher," Mr Kingwill said. "Where we are it's broadacre cropping. But the market now is driving significantly more per megalitre from horticulture than you can get a profit margin out of wheat and barley," he says.

Across the world, speculators are increasingly looking to water as a new profit engine as supplies dwindle, caught between booming populations demanding more access and climate warming threatening its very availability.

Australia, the most parched inhabited continent, has for 25 years had an internationally unique water market to better share supplies among farmers and reverse years of allocating more water than the country's rivers and dams could spare.

That market last year traded $1.1 billion in permanent and seasonal water rights, according to Mark Siebentritt, the operations manager for national water broker Waterfind, who says business last year grew by 20 per cent.

But Mr Kingwill, whose corporatised farm lists on the Australian Stock Exchange, says prices are being pushed up by a metaphorical gold rush, luring bankers and speculators both at home and internationally to a new and waterlogged Elysian field.

With drought gripping some areas for a decade, prices for one megalitre of seasonal water - enough for an Olympic-size pool - are peaking at A$600 ($517), while permanent water entitlements are less volatile, but still pricey at up to A$2,500 a megalitre. "You've got from the biggest financial institutions down to aunty Jane buying 10 megalitres of water... It's now an asset, just like a block of land, and people are buying on a daily basis," Mr Kingwill says.

While Australia has the most mature water market, it is stunningly complex, drowning in around 10,000 rules and the regulation of four states spreading over the huge food bowl Murray-Darling river basin in the continent's southeast.

The country's consumer watchdog, the Australian Competition and Consumer Commission, or ACCC, has been asked by the centre-left Labour national government to develop new and uniform rules on how water should be charged and traded.

State governments agreed in 1993 to establish a free market underpinned by a national register of water entitlements. Development has so far been hobbled by political rivalries and water over-allocation problems in some regions.

"What we want to do is to see water trading freed up so it can trade not only across regions, but also across state borders," says ACCC chairman Graeme Samuel.

But some farmers are wary of intervention by the nation's powerful regulator, fearing it will further push up prices when drought is already evaporating supplies and even major cities are enforcing tough water-saving measures like no car washing.

In July, national Water Minister Penny Wong extended the time for farmers to have a say in the coming reforms, with the ACCC to report back in December and again in June next year.

"By making it so investors can come in, there is concern the small guy on the block is not getting a fair shake. But then again, some argue that the more investors come in, they drive the value up. The arguments go on forever," says Mr Kingwill.

Waterfind's Mr Siebentritt says his business has been tracking water trade for 20 years and has developed an electronic platform which automatically matches registered buyers and sellers, advising which areas are legally entitled to trade.

Mr Kingwill's Tandou, which has more land under water-saving subsurface drip irrigation than any other farm in Australia, is a client, with a sizeable ability to store water.

But Mr Siebentritt does not see water making the transition anytime soon to a pure investment rather than a public right overseen by government and used 70 per cent for agriculture.

"There's some speculation, but people investing in water now are doing it as a way of investing in agriculture," he says.

"What drives the price is the value of the produce that can be grown with the application of that water, so really the price of commodities on international markets - whether it be food or rice or cotton - is having an impact on the value of water," Mr Siebentritt says.

Wendy Craik, in charge of managing food bowl water through the Murray-Darling Basin Commission, said there has been an "explosion" on the water market in recent years, with around 30 per cent of all available water traded.

"We're seeing corporate groups getting together and purchasing water, and then having an arrangement with farmers where they provide the water to produce a crop," Ms Craik says.

"There are stories of some of the banks getting in there and buying water for agribusiness," she says.

ACCC involvement, Ms Craik says, will streamline and regulate a water trade system that has evolved over a quarter century from a semi-informal dealing between farmers in separate river valleys, but given new urgency by scarcity, climate shift and drought.

"Government will always have a pretty close eye on water, simply because water has become more critical," Ms Craik says. "Currently buying a house has a lot of paperwork, but buying a piece of water has a lot more."

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