Of the world's known petroleum reserves, 65 percent lie beneath the Middle East, where supplies could be exhausted in about 85 years if no new reserves are found. But the most critical resource here is water, which has contributed to past conflicts and may one day start others. A key issue dividing Israel and its Arab neighbors, for example, is control of the tributaries of the Jordan River and West Bank aquifers. Across the region, recycling of wastewater and drip irrigation, along with dam reservoirs and desalination, could help relieve shortages. With few regional water agreements and the growing threat of pollution, the most fundamental problem, though, is scant and undependable rainfall. Without oil, the Middle East cannot live well; without water it cannot live.