When Ibrahim, on God’s orders, refrained from sacrificing his son Ishmael and sacrificed a sheep instead, the blood spurted skyward and created the Milky Way. Drops also rained down on the earth and created the water sources, a gift of God.

You can still hear this tale from Bedouin in Sinai, says an anthropologist who asked to remain anonymous. She hasn’t heard a similar story from Palestinian Bedouin, but they, too, were raised on its ethical and practical implications: Because water sources, like rivers and springs, are a gift from God, one may not privatize, fence off or block access to them. And because they belong to everyone, they must be used fairly: Tents must be pitched a few hundred meters from a river or spring, so as not to pollute them and not to deter others from using them.