LONDON — After he signed the Egyptian-Israeli peace treaty in 1979, Egyptian President Anwar Sadat said: "The only matter that could take Egypt to war again is water." Well, the world kept turning, and now a potential war over water is creeping onto Egypt's agenda.

Egypt is the economic and cultural superpower of the Arab world: Its 78 million people account for almost a third of the world's Arabic-speaking population. But 99 percent of it is open desert, and if it were not for the Nile river running through that desert, Egypt's population would not be any bigger than Libya's (5 million). So Cairo takes a dim view of anything that might diminish the flow of that river.

In 1929, when the British empire controlled Egypt, Sudan and most of the countries further upstream in East Africa, it sponsored an agreement giving Cairo the right to veto any developments upstream that would decrease the amount of water in the Nile. The rationale at the time was that the upstream countries had ample rainfall, whereas Egypt and Sudan (at the time ruled as one country) depended totally on the Nile's waters.