Consumptive uses and losses

Overview

Editorial Note, 25 February 2026: In the past few years, Reclamation has made significant changes in how Upper Basin and Lower Basin CUL are calculated and reported; see below for more details. We have removed a figure and several paragraphs on this page that summarized basinwide CUL values, since they reflected the previous, outdated data. We hope to add new summary information to this page in the future. We have also revised the Data and tools section below; further revisions are likely.

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.

Reclamation reporting of consumptive uses and losses (CUL) data

Consumptive uses and losses (CUL) reports and data are prepared by Reclamation pursuant to the Colorado River Basin Project Act of 1968 (Public Law 90-537). They present estimates of anthropogenic consumptive uses and losses for the Colorado River System for each calendar year from 1971 and the data are categorized by type of use, reporting area, and by individual state.

In 2024-25 Reclamation made significant changes in how Lower Basin CUL data are calculated and reported, and has recalculated historical CUL data for the Lower Basin. Over the same period, Reclamation implemented an improved method for estimating agricultural consumptive use in the Upper Basin, and likewise recalculated historical CUL data for the Upper Basin. Reclamation has developed interactive visualization tools for the recalculated CUL data and as of February 2026, is preparing the full set of 5-year reports based on the recalculated CUL data.

Annual data for the Upper and Lower Colorado River Systems are calculated and reported by Reclamation’s respective regional offices, and joint reports covering five-year periods are published with system-wide summaries. Methodologies between the two basins are generally consistent, with any differences highlighted in either the Upper Colorado Basin Region’s Methodology Manual, or the Lower Colorado Basin Region’s Methodology Manual.

Important considerations for interpreting Reclamation’s CUL Data:

1. Only anthropogenic uses and losses are reported. As such, natural evapotranspiration, (e.g. from riparian areas) and losses (e.g. natural lakes/river evaporation) are not reported in this dataset.
2. Lower Basin data include mainstream and tributary uses (see map). Mainstream data are derived from Reclamation’s annual Colorado River Water Accounting Report and do not use the same methods as the tributary areas.
3. Use categories (agriculture, municipal and industrial, thermal electric power, etc.) are assigned only to water used within the boundary of the Colorado River System. As such, water that is exported out of the system is reported as an export and not assigned a more specific use category.
4. Reclamation’s Upper and Lower Basin CUL webpages now offer downloadable machine readable data products that provide CUL data monthly, by use category at a State, Hydrologic Unit Code (HUC) 8 spatial level.

Data and tools

Reclamation CUL reports and data

New and recalculated CUL data:

• Upper Basin CUL Webpage

• Lower Basin CUL Webpage

• Upper Basin CUL Data Visualization Tool, 1971-2024

• Lower Basin CUL Data Visualization Tool, 1971-2024

Also, since 1964, Lower Basin diversions and consumptive uses, and deliveries to Mexico, have been summarized in the annual Water Accounting Reports, but these reports do not contain estimates of Lower Basin reservoir evaporation or other losses.

• Lower Basin Annual Water Accounting Reports (1964–2024)

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.