Consumptive uses and losses
Overview
NOTE: In 2024-25, Reclamation made significant changes in how Lower Basin CUL are calculated and reported. In late February 2026, a figure and several paragraphs on this page that summarized basinwide CUL values were removed as they reflected previous, outdated data. New summary information will be added to this page later in 2026.
Knowing how much water is being used–and for what purposes–is central to water resource management. Accurately quantifying use can be challenging at the scale of the individual water user, especially in agriculture. In gathering water use data at the basin scale, these challenges are compounded by the varying uncertainties in quantification across uses, inconsistent reporting, and variable terminology.
The terminology used in reporting by Reclamation and the basin states is consumptive uses (CU) and losses. The combination of these two terms, sometimes abbreviated as CUL, is the counterpart to supply in the water-balance equation.
Consumptive uses refers to water that is diverted from a stream or river for any beneficial use (agriculture, municipal use, power-plant cooling, etc.), minus any return flows that would then be available to a downstream user on that same stream or river. When water is diverted from the Colorado River and used in another basin (e.g., Colorado’s Front Range), then the entire diverted amount is treated as consumptive use with respect to the Colorado River, since any return flows would take place in a different river system.
Losses refers to depletions of water apart from beneficial uses; in the Colorado River Basin losses come primarily from (1) reservoir evaporation and (2) transit losses. The latter is the loss of water to evaporation and phreatophytic vegetation within and adjacent to the river channel, the mainstem below Lake Mead. Seepage into, and storage within, the river banks is not treated as a loss, since the water is likely to return to the channel later in time or further downstream.
Data and tools
Reclamation reporting of consumptive uses and losses (CUL) data
Consumptive uses and losses (CUL) reports are prepared by Reclamation pursuant to the Colorado River Basin Project Act of 1968 (Public Law 90 537) and provide 5-year reports covering major uses within each basin (Upper and Lower) of the Colorado River. The reports for the Upper and Lower basins are not prepared in parallel and contain different metrics for consumptive uses and losses.
Prior to 2006, 5-year CUL reports that covered both the Upper Basin and Lower Basin (including deliveries to Mexico) were made available. Since 2006, the 5-year CUL reports only cover the Upper Basin. Lower Basin consumptive uses and Mexico deliveries are summarized in the annual Water Accounting Reports (issued since 1964), but these reports do not contain estimates of Lower Basin reservoir evaporation or other losses.
Additional resources
Colorado River Basin Water Supply and Demand Study - Technical Report C
Technical Report C (Water Demand Assessment) of the 2012 Basin Study, in Section 2.4 summarizes historical trends (1971-2010) in basin water use, including municipal use.
Water Resource Modeling of the Colorado River: Present and Future Strategies
The Center for Colorado River Studies at Utah State U. published this 2019 overview of water resource modeling in the Colorado River. Page 33 lists the 2000-2017 averages for different components of basinwide CUL.