The risk that dwindling supplies of fresh water will spark bloody regional conflicts in dry regions of the world is far smaller than feared, a United Nations report said on Wednesday.

The threat of "water wars" has risen up the international agenda in the past couple of years, propelled by warnings from thinktanks and political leaders and by tensions in the Middle East, the region that suffers from the worst water scarcity.

But according to the UN study, the World Water Development Report, wars triggered by water disputes are historically rare and there are good reasons for thinking the future will be no different.

"Despite the potential for dispute in transboundary (river) basins, the record of cooperation historically overwhelms the record of acute conflict over international water resources," the World Water Development Report says.

In the past 50 years, it says, there have been only 37 cross-border disputes which have involved violence, while some 200 treaties on water-sharing have been negotiated and signed.

This implies countries realise that "violence over water is not strategically rational, effective or economically viable," according to the study.

The document was drawn up by the World Water Assessment Programme, an association of 23 UN agencies that is hosted by the Paris-based agency UNESCO.

It was published on Wednesday ahead of the Third World Water Forum, a major conference on the future of the world's fresh water supplies, taking place in Kyoto, Japan, from March 16-23.

Overall, the report paints a pessimistic outlook about water problems, saying the world's population will surge over the next two decades while the availability of fresh water, hit by pollution and waste, would shrink.

Many of the countries that will face a water crunch are located in the Middle East, Africa and South Asia, where there is a record of chronic instability and exchanges of blows.

But the report contends that water can be "both an irritant and ... a unifier" between countries that are at loggerheads.

A good treaty overseen by a strong institution can ensure that water is shared wisely and can also create an enduring bond, it argues.

It gave the example of the 1960 Indo-Pakistani treaty on sharing the water of the Indus, which has survived two wars between the two neighbours; the Mekong Committee, which has functioned since 1957 and exchanged data throughout the Vietnam War; and the Nile Basin Initiative, an "extremely promising" scheme launched in 1999 gathering all 10 riparian, or river-bank, states along the world's longest river.

"Once international institutions are in place, they are tremendously resilient over time, even between otherwise hostile riparian nations, and even when conflict is waged over other issues," the World Water Development Report says.

It cautions, however, that "hydrodiplomacy" is a relatively new political field, and a lot more needs to be done to avert and defuse future conflict.

Water treaties need to be flexible, identifying not only volumes of water extraction per capita, but also water quality and measures that should be taken in the event of droughts.

And, it warns, almost nothing has been done about cross-border sharing of aquifers, the groundwater that is contained in spongey underground rock which, in some of the drier parts of the world, is being run down at an alarming rate.

The report comes just a year after UN Secretary General Kofi Annan, on World Water Day in 2002, warned national rivalries over water resources could contain "the seeds of violent conflict." In the past six months, Israel has made several warnings it could strike Lebanon for tapping water from the Wazzani River, which provides up to a quarter of the inflow to the Sea of Galilee.

In 2001, the consultancy PricewaterhouseCoopers said wars over water would loom in the next few years, "just as war over fire sparked conflict among early prehistoric tribes." - Sapa-AFP.