Once World War II ended, the State of Arizona again turned its attention to the issue of water. The 1940s saw several pieces of federal legislation passed that would have a long-term effect on Arizona's water supplies. The Mexican Water Treaty of 1944 allotted to Mexico a guaranteed annual quantity of 1.5 million acre feet of water from the Colorado River, plus additional or less deliveries in specific circumstances.
In 1944, the State of Arizona finally ratified the Colorado River Compact of 1922. It entered into a contract with the Secretary of the Interior for delivery of 2.8 million acre feet of Colorado River water annually.
Three years later, Arizona first sought authorizing legislation for the Central Arizona Project. The Department of the Interior's project planning report was formally submitted to Congress in late September of 1948, having been found to be economically feasible by Secretary Krug. Estimated benefits from the project, designed to meet Arizona's critical water shortage and ease the southwestern power shortage, would exceed the estimated $738,408,000 cost by 50 to 60 percent.
"The showing in the report of the availability of a substantial quantity of Colorado River water for diversion to Central Arizona for irrigation and other purposes is based upon the assumption that the claims of the state of Arizona to this water are valid," Secretary Krug said in his letter of transmittal.
But California opposed it and the proposal went nowhere. Not for another 20 years would the matter of Arizona's claims on the Colorado River's water, its disputes with California, and the viability of the Central Arizona Project be determined.
On October 11, 1948, Arizona signed the Upper Colorado River Basin Compact along with Colorado, New Mexico, Utah, and Wyoming. The Compact granted Arizona 50,000 acre feet of Colorado River water from the Upper Basin. In addition, the Compact created the Upper Colorado River Commission.
Source: The Reclamation Era, November 1948
More information about the Treaty with Mexico: