available water distributed according to the:
as a percentage of:
Water allocation amongst the states in the Colorado Basin and Mexico is governed by a series of laws and treaties collectively referred to as the "Law of the River." The maximum legal allocation was based on an assumed average flow of ~16.5maf, an amount now understood to be higher than the long-term average.
In surplus years, excess water is generally stored in Lake Powell and Lake Mead for future use by the Lower Basin states. Upper Basin states are not permitted to withhold water that they are not capable of using.
The Bureau of Reclamation calculates consumptive use data for the Colorado Basin states -- meaning, how much Colorado River water do they each use in a given year. The data are calculated retroactively and availability is somewhat limited. For this map, we are using an average of the annual consumptive use data for each state since 2003. Data for the Lower Basin are from 2003-2010; for the Upper Basin, the Bureau has published data through 2015.