Wyoming became the first state in the union to claim state ownership of water when the State Constitution became effective upon entering statehood in 1890. Wyoming's water law is based on the prior appropriation doctrine. Wyoming's first territorial engineer and state engineer, Elwood Mead (who became Commissioner of the U.S. Bureau of Reclamation in 1924 and for whom Lake Mead was named) was mainly responsible for writing Wyoming's water laws. It has not been found necessary to change much in those laws during the 125 years since the Territorial Engineer’s Office was established.   Wyoming's water laws have provided the basis for laws governing water appropriation and use in many other western states.

With an average elevation of 6,400 feet (second in the nation) and the Continental Divide parsing the state into four major drainage quadrants, Wyoming is a headwaters state.  Accordingly, Wyoming is a party to seven interstate compacts and two U.S. Supreme Court decrees which govern her rights to beneficially use water, including the Colorado River Compact of 1922 and the Upper Colorado River Compact of 1948, which apportioned 14 percent of the Upper Basin water supply to Wyoming’s users in perpetuity.