for any one of its owners to erect a bridge over it, nor to raise its water in order to operate a mill there, except with the consent of all its owners, since they jointly own what no one of them may use exclusively. Likewise, in a shared alley, no one may open a door onto it, project an upper-story extension over it, or construct a covered passage above it without the consent of them all.
Aḥmad indicated this ruling in the narration of Ṣāliḥ. He was asked about a river fed by springs, from which water emerged at a measured level. The water belonged to known people who owned lands both above and below the city. Those whose estates lay above the city needed to draw water from there for their lands, but this caused harm to the inhabitants of the city. He said: “If these people own the river, having dug it and spent money on it, no one may prevent them. But if this has always been the established state of affairs, the people may prevent them until everyone receives water as they used to.”
Thus, he expressly ruled that if the river belonged to them, its use was governed by whatever they had agreed upon, and none of them could act independently with any part of it.
Their methods of taking water then fall into three categories. The first is that they take turns by days when they are few, and by hours when they are numerous. If they dispute the order, they draw lots until the order of the first person and those who follow him is settled. Each person then has exclusive use during his turn, with no one else sharing it, after which the others take their turns according to the order they established.
The second is that they divide the mouth of the river across its width with a plank extending from one bank to the other. Openings are made in it in measured proportions corresponding to their water rights, so that each opening admits the amount to which its owner is entitled—one-fifth, one-tenth, or whatever the proportion may be—and he conveys it to his land in turn.
The third is that each of them digs, opposite his land, a water outlet of a measure fixed by their agreement or in proportion to the size of their properties. He then takes from the river the amount corresponding to his right, in equal proportion with all his partners. He may not increase it, nor may they reduce it. None of them may postpone a water turn that was assigned earlier, just as no one who owns a shared alley may postpone a door that was assigned earlier. Nor may he advance a later water turn, even though he may advance a later door, because advancing a later door merely restricts use to part of one’s right, whereas advancing a later water turn entails taking more than one’s right.
As for the protective zone of this excavated river in uncultivated waste land, it has been said that it is determined according to customary practice in comparable cases. The same applies to a qanāt, since a qanāt is an underground river. It has also been said that the protective zone of a river is the place where its excavated mud is deposited; and it has been said that the protective zone of a qanāt is the area where the water does not flow over the surface of the ground and which serves to collect it. We have stated concerning the protective zone of land reclaimed for habitation or cultivation that it is determined by whatever that land cannot do without in terms of access and open space.