The supply of water is a matter of life and death, war and peace for the peoples of the Middle East.

Israel is likely to face a shortage of water for drinking and for agriculture because of recurrent droughts, an increase in consumption, and pollution. Moreover, territorial compromise with its neighbors could put as much as half its water supply at risk. This makes securing its existing supplies and developing new ones vital for its future prosperity. Consequently, water is a key element of any peace negotiation, but it is widely neglected in the public debate.

Syria’s foreign minister has said that “Israel has no right even to a single drop of water.” If Syria controlled the Golan Heights, it could divert water flowing into the Sea of Galilee, which supplies about 25% of Israel’s water. The effort to do so between 1965 and 1966 was one of the causes of the Six-Day War.

Syria could severely compromise Israel’s water supply even if its intentions were not malevolent. For example, increasing the population in the area would produce sewage and other contaminants that could pollute the Sea.

Any peace treaty would have to ensure Israel’s water rights, but can Israel afford to put one-quarter of its water supply at the mercy of a foreign power, especially one whose leaders have talked about denying Israel all “Arab water”? Ultimately, Israel may have to choose between water and peace with Syria.

Israel’s water security is further threatened by the fact that the mountain aquifer, which supplies another 25% of Israel’s water, including most of the drinking water for the major cities, is partially located in the West Bank. Even if a future Palestinian state had peaceful intentions, it could significantly reduce the water available to Israel because of the desire to satisfy the needs of its own population.

Today, unauthorized Palestinian drilling of wells in the West Bank affects the quality of the aquifer. Without any other water source, the Palestinians will be tempted to pump more out of the aquifer to meet their needs and thereby inundate it with seawater.

The poor quality of Palestinian Authority water treatment facilities, mismanagement, neglect, and the low priority placed on environmental issues increase the likelihood that the aquifer will be polluted and its quality reduced perhaps to the point of being undrinkable. This has already occurred in the Gaza Strip where the sole aquifer is unusable because of contamination and salinity.

To secure its water future, Israel would need to maintain control over three West Bank regions comprising 20% of the land. In return, Israel has said it is prepared to give up control of the mountain aquifer. This would make Israel dependent on the goodwill of the Palestinians to protect the quality of the water and to ensure that Israel continues to receive sufficient water to meet its needs.

One reason for optimism is that Israelis and Palestinians have made efforts to protect the water supply. In 2001, the two parties issued a joint call to refrain from harming the water infrastructure and water supply to both Israelis and Palestinians. Israel has also resisted the temptation to use water as a weapon and continued to supply water promised to the PA.

If Israel sees its water supply or quality endangered, it will have to decide whether to take military action to stop the drilling of wells, divert the water, or to seize the water source. What level of provocation would the United Nations or America find sufficient to justify Israeli action? What, if anything, would those parties be prepared to do to prevent the interdiction of Israeli water supplies?

The historical answer to that question is not encouraging.

The most popular idea for alleviating Israel’s water shortage is desalination. In 2000, Israel launched the Desalination Master Plan that envisioned the construction of a series of plants along the Mediterranean coast. The first of these was built in Ashkelon in 2005. The plant is expected to provide approximately between 5% and 6% of Israel’s total water needs.

Desalination is not a panacea. It can ameliorate Israel’s water problems, but not solve them. The plants are expensive, take a long time to build, use a lot of energy, and will not supply as much water as Israel will need. They also make tempting targets for terrorists.

King Hussein of Jordan once warned that the one issue that could lead him to go to war again is water. A water sharing arrangement was a key feature of the treaty Israel signed with Jordan.

The complexity and volatility of the issue have led the Israelis, Syrians, and Palestinians to postpone serious discussions of future water sharing arrangements. To insure that water does not become a flashpoint for conflict, however, negotiations among Israel and its neighbors must take into account water security.

Their lives depend on it.

Mr. Bard is the executive director of the American-Israeli Cooperative Enterprise, director of the Jewish Virtual Library, and one of the leading authorities on U.S.-Middle East policy. He has written and edited 18 books including “Will Israel Survive?” recently released.