Water Use and Accounting

All water use and accounting reports are available for download from the U.S. Bureau of Reclamation’s Lower Colorado River Water Accounting page.

Overview

The U.S. Bureau of Reclamation regularly compiles and publishes detailed quantitative accounting of water in the Lower Colorado River, regularly issuing its Water Accounting Report and Consumptive Uses and Losses Report. CRB regularly provides feedback to the U.S. Bureau of Reclamation on all of its related activities, including reviewing its related reports for quality and accuracy.

Background

A full and accurate accounting of water in the Colorado River Basin is critical for managing the Colorado River. To achieve this, the U.S. Bureau of Reclamation, as required by law and in consultation with basin stakeholders, regularly publishes the following two reports:

In addition, Reclamation has previously published the Lower Colorado River Annual Summary of Evapotranspiration and Evaporation (LCRAS) Report to inform water accounting. Each of these reports are summarized below, described in further detail by Reclamation on its History and Types of Reports page. They are available for download from its main Lower Colorado River Water Accounting page, with recent versions provided here.

In addition these reports, Reclamation also regularly publishes forecasted and actual water use and water schedules and approvals on its Lower Colorado River Water Accounting webpage.

Water Accounting Report

The Consolidated Decree of the U.S. Supreme Court in Arizona v California (547 U.S. 150 (2006)), Section V, requires the Secretary of the Interior to:

prepare and make available … complete, detailed, and accurate records of:
(A) Releases of water through regulatory structures controlled by the United States;
(B) Diversions of water from the mainstream, return flow of such water to the stream as is available for consumptive use in the United States or in satisfaction of the Mexican Treaty obligation, and consumptive use of such water.

Formally called the “Colorado River Accounting and Water Use Report: Arizona, California, and Nevada”, the Water Accounting Report implements the above requirement of the Consolidated Decree, by tabulating measured diversions, measured and unmeasured returns, and consumptive uses of each user taking water from the mainstem of the Colorado River below Lees Ferry.

First published in 1964 as required by Arizona v. California (1964), the Water Accounting Report has since been substantially revised to accommodate changing accounting needs. The report now also tabulates water quantities related to, among others:

  • off-stream storage/interstate water banking;
  • the Lower Colorado Water Supply Project;
  • transfers made under the Colorado River Water Delivery Agreement (aka the 2003 Quantification Settlement Agreement or QSA);
  • Inadvertent Overrun and Payback Policy (a component of the QSA); and
  • Intentionally Created Surplus.

Consumptive Uses and Losses (CUL) Report

The Colorado River Basin Project Act (82 Stat. 885), Section 601(b), requires Reclamation to report on the annual consumptive uses and losses (CUL) from the Colorado River System every five years, with the first five-year period starting on October 1, 1970. The Consumptive Uses and Losses Report implements this requirement, reporting CUL quantities for the mainstem and tributaries of the Lower Colorado River, most recently for the Water-Year (WY) 1971-2005 period. Mainstem CUL are reported at the state level. Colorado River water used/consumed outside of the Lower Colorado River hydrologic basin–including that in California–is reported as bulk exports. CUL reporting areas for the Lower Colorado River are shown in the figure below.

A map of the Lower Colorado River region showing reporting areas for consumptive uses and losses.
Lower Colorado River System reporting areas in the Consumptive Uses and Losses Report. Source: 1971-2005 Lower Colorado System CUL Recalculated Report (pdf).

In 2024, Reclamation recalculated the 1971-2005 Lower Colorado System CUL with improvements in the calculation methods, then applied the recalculation approach to the 1971-2015 period. Related reports are available from the links on the right or from Reclamation’s Lower Colorado River Water Accounting page.

Lower Colorado River Annual Summary of Evapotranspiration and Evaporation (LCRAS) report

From 1995 through 2014, Reclamation provided estimates of annual agricultural, riparian vegetation, and open water acreages and water uses along the lower Colorado River from Hoover Dam to the Southerly International Boundary (SIB) with Mexico. Although new reports are no longer generated, the calculations from previous reports continue to inform water accounting in the Lower Basin.