Water is the most valuable resource in the Middle East, more precious even than oil.

Scarcity of water has contributed to regional tensions and is an aggravating factor in the Arab-Israeli conflict:

• Israel and the Palestinians: The conflict between Israel and the Palestinians is about water, as well as land. The West Bank is a major source of water for Israel. But Palestinians complain that, on average, an Israeli uses three times as much water as a West Bank Palestinian.

• Lebanon: The Lebanese have long accused Israel of having designs on the waters of the River Litani, suspecting this is one reason why the Jewish state maintains a toehold in southern Lebanon. Israel denies the charge.

• Syria: Similarly, Syria accuses Israel of being reluctant to withdraw from the Golan Heights - the strategic plateau it captured in the Arab-Israeli war of 1967 - because of a desire to exploit the Golan's water resources.

• Egypt: Cairo warned, in 1991, that it was ready to use force to protect its access to the waters of the Nile. The warning was directed mainly at its neighbours Ethiopia and Sudan. Rapid growth of a population already over 60 million is putting immense pressure on Egypt's water supplies.

• Turkey: Turkey's exploitation of the waters of the Euphrates has long been controversial. Since 1984 the Turks have been building a series of dams and hydropower plants in south-east Turkey, as part of an ambitious scheme known as GAP. Syria and Iraq complain the scheme is depriving them of much-needed water. Given the troubled relationship between Syria and Turkey, in particular, the issue has become politically contentious.

For example, water is one of the issues on the agenda of the multilateral peace talks that are - in theory - an integral part of the Middle East peace process.

But, in practice, the issue continues to be divisive. States routinely use water as a bargaining chip in their quarrels with neighbours.