Global warming, growing populations and meat eating habits are exacerbating the world's precarious water situation. A major part of this problem is that meat eaters consume the equivilent of five times the amount of water used by people on vegetarian diets. As countries like China and India develop larger middle classes, more and more of them are switching to a western diet that includes much more meat.

The consensus emerging among scientists is that it will be almost impossible to feed future generations the typical diet eaten in western Europe and North America without destroying the environment.

A meat and vegetable diet, which most people move to when economically possible, requires more water than crops such as wheat and maize. On average, it takes 1,790 litres of water to grow 1kg of wheat compared with 9,680 litres of water for 1kg of beef.

Says Anders Berntell, the director of the International Water Institute; "The world's future water supply is a problem that's ... greater than we've begun to realize.

"We've got to reduce the amount of water we devote to growing food. The world is simply running out of water."

Global warming is worstening the water supply situation by melting glaciers that people have been relying on to supply water. For example, global warming is shrinking China's highland glaciers, including those covering Mount Everest, by an amount equivalent to all the water in the Yellow River every year.

Much of the melted glacier water vaporizes long before it reaches the country's drought-stricken farmers and again global warming is to blame.

The human cost could be immense, since 300 million Chinese live in the country's arid west and depend on water from the glaciers for their survival.

All of this has lead some scientists to speculate that water wars could break out in the future over dwindling water supplies.

"We have had oil wars," said Professor William Mitsch. "That's happened in our lifetime. Water wars are possible."

Scientists at the World Water Week conference which began on Sunday in Stockholm said that ignorance and complacency were widespread in wealthier countries.

"I don't know what will shake these regions out of complacency other than the fact there will be droughts, pestilence and wars that break out over water rights," said Mitsch, professor of natural resources at Ohio State University.

Mitsch told Reuters potential flashpoints included the Middle East.

"Continuing on our present path will mean more conflict," a report by International Water Management Institute (IWMI) said.