"It's necessary that we raise awareness that food requires a lot of water," Anders Berntell, head of the Stockholm International Water Institute (SIWI), told Reuters during a conference hosted by SIWI of more than 1,000 water experts.

"Some kind of labelling of food products when it comes to their water requirements could be a first step," he said. "Then people could see for themselves." Labels might, for instance, highlight water needed for irrigation beyond natural rainfall.

A UN-backed report released in Stockholm on Monday said that one in every three people lives in regions with water shortages. And it projected that demand for water, led by irrigation, was likely to almost double by 2050.

Berntell said most efforts to curb water use focused on more efficient use of water in irrigation, which takes about three quarters of all water used by humans, rather than on ways to encourage consumers to review their diets and lifestyles.

With labels "if there is a choice between an entrecote or a chicken filet or a fish -- which requires almost no water because it lives in the water anyway -- then you could make a more enlightened choice," Berntell said.

MILK, VEGETABLES

"Producing meat, milk, sugar, oils and vegetables typically requires more water than cereals," the UN-backed report compiled by the International Water Management Institute said.

Berntell said that he knew of no countries planning water labelling of foods.

In a more extreme scenario, Berntell said arid countries might even face trade barriers if they exported water-intensive crops. Such controls on "virtual water" were unlikely ever to be applied but were worth debating to help promote efficiency.

Australia, for instance, exports meat to countries where water is far more plentiful. "Some Australians ask 'how can our arid country export scarce water to other water-rich parts of the world?'" he said.