Imagine that a group of friends are camping in a hot and dry place with one container of water. The water is necessary for drinking, cooking, and washing. The group must decide the how much each person will receive and for what purposes the water will be used. The individual portion of water is called a water allotment. The laws that govern to whom water allotments are given, and for what purposes water allotments are used, are called water rights. A water right is a use of water or a water source. Everyday, large nations and small communities alike must decide how to allocate their available sources of water. Negotiations similar to those in the camping example are conducted between individuals, cities, and countries to decide who has rights to water on a nation's land or within its borders.

In the United...