Municipal water use

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Overview

Figure 1. Major cities within the Colorado River Basin, and outside of the basin (red hatching), that receive at least part of their municipal water supply from the Colorado River and its tributaries. (Source: Figure ES-1 in Municipal Deliveries of Colorado River Basin Water, M. Cohen, Pacific Institute, 2011)

Colorado River municipal water use (i.e., residential, commercial, industrial, and institutional uses within towns and cities, aka municipal and industrial or M&I) 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. 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. Nearly all of these cities outside the watershed use additional water sources and do not rely entirely on the Colorado River and its tributaries.

While the U.S. cities that depend in full or in part on Colorado River water have, with few exceptions, experienced rapid population growth over the last 20-30 years, per capita water use has broadly and significantly declined over that same period. The work by Richter (2023) linked in Data and tools below indicates that Denver and other large cities in Colorado reduced their per capita water use by 20-40% from 2000 to 2020, with similar reductions in Salt Lake City (30%), Albuquerque (40%), the Phoenix area and Tucson (10-30%), and southern California (30-40%), and greater Las Vegas (47%). For most of these cities, this per-capita reduction has exceeded population growth, and overall water use, from all sources, has declined since 2000.

The recent change in these cities' total use of water specifically from the Colorado River is more mixed, since a number of them have shifted their sources since 2000 and have become more reliant on Colorado River water (e.g., several Phoenix suburbs, Tucson, San Diego), while other cities have shifted sources away from the Colorado River (e.g., greater Los Angeles). In aggregate, municipal use of the Colorado River, at least in the U.S., has stayed relatively constant since 2000 (see Figure 1 in Consumptive uses and losses) even as the total population served by the river's water increased by over 20%. But this can also be put the other way: basin-wide, population growth and the shifting of water sources has canceled out the gains from widespread reductions in per-capita water use.

The municipal use of water is highly seasonal, with a pronounced peak in the warm season, since about half of all municipal use is used to irrigate plants--grass lawns, trees, and other urban greenery. This component of municipal use, like agricultural use, is sensitive to weather and climate, typically increasing during warmer, drier periods if not checked by municipal restrictions or other constraints. Further warming of the climate will tend to drive municipal outdoor use upwards, as evapotranspiration (ET) losses increase, in the absence of changes in watering practices or the extent and type of urban greenery.

The effects of climate change notwithstanding, further reductions in municipal per-capita use may occur through the broader implementation of conservation measures such as "cash for grass" (payments for lawn removal), permanent restrictions on watering, and direct reuse of wastewater.

Cities using Colorado River water

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. About 300,000 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 south 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. Most of these diversions are used for agriculture with only a small percentage going towards 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

Virtually all of Arizona is within the Colorado River Basin. The major cities in central and southern Arizona primarily receive water deliveries from the Central Arizona Project (CAP; Phoenix area and Tucson) and the Salt River Project (SRP; Phoenix area). Although the Salt River is a tributary of the Colorado River via the Gila River, SRP's water uses (and supplies) do not administratively count towards Arizona’s Colorado River allocation.

Nevada

More than 75% of Nevada’s population lives in greater Las Vegas (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 receive municipal water from the Colorado River in California than in any other state. Metropolitan areas served by the Colorado River Aqueduct managed by the Metropolitan Water District of Southern California (MWD), including greater Los Angeles and San Diego, have used between 0.5 and 1.1 million acre-feet of Colorado River water per year in the period 2017-2021, with the amount of use largely depending on the yield from MWD's other water sources. The Coachella Valley Water District and Imperial Irrigation District, while primarily serving agricultural use, also deliver water to numerous municipal water agencies in their respective valleys.

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

Richter (2023) study and data on Colorado River municipal water use

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.


Additional resources

Municipal Deliveries of Colorado River Basin Water

The Pacific Institute published this 2011 report that provides 1990, 2000, and 2008 population and water delivery data and trends for cities that use water from the Colorado River basin.

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.