Municipal water use
Overview
Colorado River municipal water use (i.e., residential, commercial, industrial, and institutional uses within towns and cities) accounts for about 25% of the beneficial uses of the Colorado River and about 20% of all consumptive uses and losses. These municipal uses occur in both cities within the Colorado River Basin such as Las Vegas, Phoenix, and St. George, UT, and in many cities outside the physical watershed, including Denver, Salt Lake City, Los Angeles, and Tijuana. Most of the cities outside the watershed use additional water sources and do not fully rely on the Colorado River and its tributaries.
Of the 40 million people receiving at least some of their municipal water from the Colorado River, an estimated 70% live outside of the river basin, mostly in Southern California, and so that water is delivered via trans-basin diversions. While the cities reliant on Colorado River water have grown rapidly over the last 30 years, per capita municipal water consumption has generally decreased over that period, so that total water use for each city has either declined, such as in Las Vegas and Denver, or has grown more slowly than the population.
Relevance
Colorado
The vast majority of the municipal water use of the Colorado River within Colorado occurs out-of-basin, in the Front Range urban area that is anchored by Denver. Over 400,000 acre-feet of water are diverted annually from the headwaters of the Colorado River and conveyed east across the Continental Divide to cities spanning from Fort Collins and Greeley to Pueblo. Within the basin, virtually all towns and cities on Colorado’s Western Slope rely on water from the Colorado River or its tributaries, including Durango, Montrose, and Grand Junction.
Wyoming
Municipal use of Colorado River water in Wyoming is relatively small compared to the other basin states. The largest single diversion and use is the ~ 20,000 acre-feet annually exported from the Little Snake River across the Divide to Cheyenne. The largest of the handful of Wyoming cities within the basin that rely on Colorado River water are Rock Springs and Green River.
New Mexico
New Mexico’s municipal use includes water from tributaries in both the Upper and Lower Basins. In the Upper Basin, the San Juan River flows through and provides water to Farmington, and also is the primary source of water for the San Juan-Chama project. This project exports water from the Colorado River basin for agriculture and municipal uses in the Rio Chama basin of the Rio Grande. About two-thirds of the exported water is allocated for municipal use in Albuquerque, Santa Fe, Los Alamos, Los Lunas, Taos, and Espanola. In the Lower Basin, New Mexico extracts groundwater from the Little Colorado and Gila River basins.
Utah
Utah’s municipal use also draws from tributaries located in both the Upper and Lower Basins. In the Upper Basin, Utah diverts water from the Duchesne River to supply the Wasatch Front near Salt Lake City. Despite the geographic proximity to Salt Lake City, the majority of these diversions are used for agriculture with small percentages allocated for municipal use. In southern Utah, rapidly growing Washington County, including the city of St. George diverts from the Virgin River, and also extracts groundwater from the Virgin River basin.
Arizona
The majority of Arizona’s population lives within the Colorado River Basin in the greater Phoenix metropolitan area, often referred to as “the Valley.” Municipalities in Arizona primarily receive water deliveries from the Central Arizona Project (CAP) and the Salt River Project (SRP), both of which divert water from the Colorado River Basin. Although the Salt River is a tributary of the Colorado River, these water uses allocations are considered to be within the Gila River and do not count towards Arizona’s Colorado River allocation.
Nevada
More than 75% of Nevada’s population lives in Clark County in southern Nevada. Southern Nevada receives all of its water from the Colorado River basin and its groundwater; 90% of its water is from surface waters in the Colorado River basin and the remaining 10% is derived from Colorado River basin groundwater.
California
More people rely on Colorado River water in California than in any other state. Metropolitan areas served by the Colorado River Aqueduct managed by the Metropolitan Water District of Southern California account for approximately 1.2 million acre feet of water per year. The Coachella and Imperial valleys are also responsible for delivering water to numerous municipal water agencies and account for additional water diversions.
Mexico
Mexicali, San Luis Rio Colorado, and Nogales all lie within the Colorado River basin and rely at least in part on Colorado River water. The Colorado River-Tijuana aqueduct exports Colorado River water to the cities of Tecate, Tijuana, and Rosarito which do not lie within the Colorado River Basin. Tijuana and Mexicali both rely almost exclusively on Colorado River water.
Data and tools
Brian Richter: Decoupling Urban Water Use from Population Growth in The Colorado River
Richter (2022) study and data on Colorado River municipal water use A 2022 study by Brian Richter included a supplementary database that summarizes municipal water use and population in 2000 and 2022. Note that the study is paywalled.
Reclamation reporting of Consumptive uses and losses (CUL) data
The Reclamation CUL Reports (since 2006, covering only the Upper Basin) contain estimates of aggregate municipal and industrial use within the Basin, based on population and assumed per-capita use. Municipal use that occurs outside of the basin (e.g., Colorado’s Front Range) is classified as “exports.” The Reclamation Water Accounting Reports (covering only the Lower Basin) breaks down consumptive use by point of diversion, which can identify the use by some of the municipalities and metropolitan areas in the Lower Basin states, but not others. See the Consumptive uses and losses page for more details and links to these reports.
Additional resources
Pacific Institute's Municipal Deliveries of Colorado River Basin Water
The Pacific Institute published a report covering municipal deliveries of Colorado River Basin water (2011). This study reports 1990, 2000, and 2008 population and water delivery data and trends for cities that use water from the Colorado River basin.
Reclamation Colorado River Basin Water Supply and Demand Study - Technical Report C
Reclamation's (2012)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.