Pure, potable water is an essential resource, second only to breathable air in importance for life on earth, but it has other valuable attributes as well. It powers industry, provides recreation, irrigates agriculture, and is a highway for ships. It also takes many forms, from oceans, rivers, and lakes to groundwater and even atmospheric moisture. Given this vital significance, water rights have been contended throughout history.

One area of frequent dispute is jurisdiction. If a water right is a right to use water, then who has the authority to grant or withhold that right? The obvious answer is the government that has jurisdiction over the territory in which the water is found. However, water pays no attention to boundaries. A river that begins in one jurisdiction flows into another. Problems arise when people in the first jurisdiction deprive people in the other of a sufficient quantity...