Biofuels, which are made from crops, require huge amounts of water, a resource that is already in short supply in many parts of the world. Bioenergy could thus end up diverting water resources desperately needed for food crops.

"When governments and companies are discussing biofuel solutions, I think water issues are not addressed enough," Johan Kuylenstierna, director of the World Water Week conference, told AFP.

The annual gathering is being attended by some 2,500 water experts from around the world.

In the future "food production will need to increase, water consumption will increase dramatically in the agriculture sector and biofuels will increase. This doesn't add up for the water perspective," Kuylenstierna added.

"Where will the water to grow the food needed to feed a growing population come from if more and more water is diverted to crops for biofuels production?" asked Stockholm International Water Institute (SIWI) spokesman David Trouba.

According to SIWI, in 2050, the amount of additional water needed for bioenergy production will be equivalent to the amount required by the agricultural sector to feed the world properly.

"Biofuels are not 'the' solution, but one of the solutions," Kuylenstierna stressed.

Meanwhile Sunita Narain, the head of the Centre for Science and Environment in India and a prominent expert at the Stockholm conference, said biofuels were "good as an idea, bad in practice."

The main priority should not be how to develop biofuels, but rather how to put a halt to society's increasing fuel consumption, she insisted.

She said it was "asinine" to believe that the world would be able to continue to consume as much biofuel in the future as it does fossil fuel today.

"If you want to use water for it (biofuel production), you must cut down on the consumption of biofuels," she said, suggesting that ethanol be used for collective transport such as buses to reduce the number of cars on the road.

In addition to the water shortage issue, experts said they also feared that large-scale biofuel production would lead to a sharp rise in the price of food staples.

"Biofuel production could be a great competitor to food production. Global food prices could increase," Kuylenstierna explained.

That thought was echoed by Narain, who criticised price pressure on foodstuffs and cited the case of the recent "tortilla war" in the United States.

An increase in US production of ethanol, made of maize, in early 2007 led to a rise in the price of the crop on the international market, which in turn prompted a surge in the price of tortillas, a corn-based bread that is a staple among Mexicans.

The United States is investing heavilyin developing its ethanol production, which now accounts for five percent of fuel volumes sold in the country.

For 95 litres of pure ethanol, some 200 kilograms (440 pounds) of maize are needed, or the equivalent of enough calories to feed a person for an entire year, SIWI noted.

All rights reserved. � 2005 Agence France-Presse. Sections of the information displayed on this page (dispatches, photographs, logos) are protected by intellectual property rights owned by Agence France-Presse. As a consequence, you may not copy, reproduce, modify, transmit, publish, display or in any way commercially exploit any of the content of this section without the prior written consent of Agence France-Presse.