“…The best way to think of this problem is as an illustration of the so-called double marginalization question, where, when the dust settles, to unrelated monopolists acting independently reduce the social gains from the utilization of their resources. 19 The basic intuition is that each of the monopolists will ignore the harms that his decision imposes on any other monopolist, so that acting separately the riparians do far worse than they would if they coordinate. This problem arises only, however, when the two monopolists stand in an upstream and downstream relationship to each other, a term that is descriptive, not metaphorical, in the water case.…”