In recent years, the western states have often struggled with the federal government over control and management of natural resources, particularly water. For its part, federal law defers to states in many matters of water resource allocation.

Reserved water rights are a major exception to this general policy of federal deference to state water law. The reserved rights doctrine provides that when the United States designates land for a particular use, it also claims enough water to fulfill the primary purposes of that designation. The reserved rights doctrine evolved in the federal courts through the 20th century, beginning with Indian reservations and later extending to other federal areas such as national forests and national monuments. By ensuring an adequate long-term water supply for these public lands, reserved water rights provide vitally important protection for ecological values and other national interests.