Fiat or custom: The checkered development of international water law

Watercourses are a vitally important sub-system of the hydrologic cycle. Their significance for transportation and agriculture was recognized far back in human history and led to the early assertion of authority by riparian states over the stretches of international watercourses that flowed through their territories. This, in turn, led to conflicts and delayed the emergence of a customary law of cooperation, including the principle that the river basin should be treated as a unity in law. If accepted, that principle would reflect the physical unity of the basin, linking its waters with other components of the hydrologic cycle.