Demand for clean water, caused by surging population growth, environment abuse and poor water management, is becoming a dangerous source of friction in many parts of the world, especially the Middle East, experts say.

The peril is being spelt out for World Water Day, a UN-sponsored event that is appealing for better international cooperation and smarter use of a precious and declining resource.

"Just as war over fire sparked conflict among early prehistoric tribes, wars over water may result from current tensions over this resource in the next few years," says a report by the consultancy PricewaterhouseCoopers.

"The Near and Middle East are the zones where there is the greatest threat," it said.

"Two-thirds of the water consumed in Israel comes from the occupied territories, while nearly half of the Israeli water installations are located in areas that were not part of its pre-1967."

Friction between Lebanon and Israel rose sharply last week after the Jewish state accused its northern neighbour of seeking to divert water from a river that feeds the Sea of Galilee, Israel's prime source of fresh water.

Other big flarepoints in the region are Turkey's plan to build dams to store the waters of the Tigris and Euphrates rivers, a scheme that is strongly opposed by Syria and Iraq; the Iraq-Iran row over the Shatt al-Arab waterway; and disputes over the use of water from the Nile, embroiling Egypt, Sudan and Ethiopia.

UN figures suggest there are around 300 potential conflicts over water around the world, arising from squabbles over river borders and the drawing of water from shared lakes and aquifers.

In southern Asia, the biggest problem is the India-Pakistan dispute over the Indus, while in central Asia "there are high risks of conflict" between Uzbekistan, Kazakhstan, Kyrgyzstan and Tajikistan over the Amu Daria and Syr Daria rivers and the already depleted Aral Sea, the PricewaterhouseCooper study said.

In Africa, the Chobe, a tributary of the Zambesi, has become a cause of tension between Botswana, Mozambique, Zambia and Zimbabwe, while there have been border incidents between Mauritania and Senegal over control of the Senegal River.

The forces behind such disputes are clear, according to the World Health Organisation (WHO), which pinpoints fast-growing population in poorer countries and water resources that are often squandered or polluted.

"Around one-sixth of the 6.1 billion people in the world lack access to improved sources of water, while 40 percent are without access to improved sanitation services," it says. Each year, 3.4 million people, mostly children, die from water-related diseases.

A UN-backed panel, the World Commission on Water, estimated last year that investment in water will have to double to 180 billion dollars a year to meet targets. Only the private sector can muster capital on this scale, it said.

World Water Day seeks this year to encourage awareness of "simple but inexpensive" measures to improve the cleanliness of water in the developing world.

One of its focuses is the tragic problem of water contamination in Bangladesh, where shallow wells have been tainted by naturally-occurring arsenic.