Thus, rivers caused to flow by Allah are unowned, as are valleys supplied by rainfall. But a well dug jointly by a group of people is privately owned.

Privately owned water is apportioned according to ownership shares, since they are co-owners and none has any priority over another. Thus, if each of two people owns one half, the water is divided equally between them. If one owns one quarter and the other three quarters, it is divided one quarter and three quarters, according to their respective shares.

The manner of distribution likewise differs. There may be a single watercourse, with distributing outlets made in it. For example, if their shares are half and half, we need two outlets; if they are three quarters and one quarter, we need four. Thus, it is apportioned as the circumstances require.

As for unowned water, the author says: “The one upstream with respect to unowned water has the right to water and to hold back the water until it reaches his ankles.” “The right to water” means that he may irrigate his crops or date palms until the water reaches his ankles. It is known that land is not level in every respect: in one area it may reach the ankles, while in another it may reach halfway up the calves. What counts, therefore, is the average level. Otherwise, if part of the land were one metre or more lower, it would take in a great deal of water before the water reached the ankles on the higher ground. Thus, the criterion is the average level.

His statement, “Then he releases it to the one next to him,” means that after he has irrigated until the water reaches his ankles, he releases it to the one next to him—unless the one upstream came later, in which case the one downstream is given precedence.