All Glossary Terms
Adjacent Areas Served (AAS)
Short for adjacent areas served by Colorado River water. It refers to locales outside the hydrologic basin of the Colorado River, where its waters are exported via transbasin diversions. Most of the population that relies on Colorado River water lives in large cities in the Adjacent Areas Served, such as Denver, Los Angeles, and San Diego. The Adjacent Areas Served, as defined in this report, generally correspond with the “adjacent areas that receive Colorado River water” as defined by the U.S. Bureau of Reclamation (2012), with two notable differences. One is the watershed of the Salton Sea, a portion of which is classified as an adjacent area by the Bureau of Reclamation because it receives Colorado River water via the All-American Canal and Colorado River Aqueduct but no longer contributes tributary flow to the river. However, before Hoover Dam was built, the Colorado River would sometimes migrate from its current channel and into the Salton Sink (see, e.g., Ross 2020). Because of that connection, we include it within the hydrologic CRB area, rather than in Adjacent Areas Served. See U.S. Bureau of Reclamation, 2012, p. ES-3. The second exception is the area in northwestern Mexico encompassing the cities of Tijuana and Ensenada. Colorado River water is exported to Tijuana via the Colorado River-Tijuana aqueduct. For our purposes this counts as an AAS, but since it is a Mexican infrastructure project, it is not included in Bureau of Reclamation service area maps. The city of Ensenada is included in this area because Tijuana sends Colorado River water there via a pipeline that was originally constructed to pump water in the opposite direction. Although in our map this area may appear contiguous with the Southern California AAS that includes San Diego and Los Angeles, it is not part of the same service area on account of the international border.
Average water consumption (or average winter consumption) (AWC)
A concept used in water budget–based rates to define tiers or blocks. It is usually calculated by estimating the average annual amount of water used by a household based on past water bills and household characteristics, or the average over the course of the winter, which typically excludes outdoor use. Those totals can determine how much water is required for basic needs and how much water use is excessive or wasteful. Generally, water budget–based rates are higher for consumption that exceeds AWC than for water use that is less than or equal to AWC. See Understanding Your Water Bill | US EPA.
Base service fee
What a community water system charges, regardless of water use. It is meant to recover costs of utility overhead such as reading and maintaining meters, carrying out billing, or other expenses. All water users incur this fee, although prices may vary by account type, meter size, location, zoning type, or use. Sometimes, base service fees include a built-in amount of usage (e.g., the base service fee might include 5,000 gallons of water before additional usage charges are incurred). Source: Understanding Your Water Bill | US EPA.
Centum Cubic Feet (CCF)
A volumetric unit community water systems apply to meter water use. One CCF is equivalent to about 748 gallons of water and is used interchangeably with hundred cubic feet (HCF). Centum comes from the Roman word for hundred. See also HCF.
Colorado River Basin (CRB)
The area drained by the Colorado River and its tributaries; a hydrologic boundary including the combined areas of the Upper Colorado and the Lower Colorado Basins. When we use the term Colorado River Basin in this study, we refer to an area that differs slightly from the HUC-02 Region shapefiles in the USGS National Hydrography Dataset (see entry for Hydrologic Unit Code). We exclude some watersheds whose tributaries do not flow directly into the Colorado River, including the Great Divide Closed Basin (HUC ID: 140402) and several basins along the Arizona-Mexico border that flow directly into the Sea of Cortez (e.g., Río Sonoita and Río Concepción). We also include a few areas that are not in the HUC-02 Region footprints of the Upper or Lower Colorado within the National Hydrography Dataset, most notably the areas around the Salton Sea and Laguna Salada in Mexico. The Colorado River, like all rivers, shifts over time. Before Hoover Dam closed, the Lower Colorado would migrate wildly and often swung westward to feed directly into the Salton Basin, hence we include that area as part of the Colorado River Basin rather than within the Adjacent Areas Served. For more, explore the Babbitt Center’s map of the Colorado River Basin.
Colorado River Basin and Adjacent Areas Served (CRBAAS)
This is the combined area of the hydrologic Colorado River Basin boundary (see CRB definition for exceptions) and the Adjacent Areas Served via transbasin diversions (see AAS definition). The CRBAAS had an estimated population of 43 million people in 2021.
Community water system (CWS)
A water utility that supplies water to the same population year-round. It serves at least 25 people at their primary residences or at least 15 residences that are primary residences. Over 286 million Americans get their tap water from a community water system. Sources: Public Water Systems | Drinking Water | Healthy Water | CDC; Factoids: Drinking Water and Ground Water Statistics for 2007, March 2008 (epa.gov).
Consumptive water use
When water is removed from available supplies without return to a water resource system. In the case of irrigation, consumptive use is the amount of water that does not flow off the field and returns to the canal or water body for re-use. Source: Consumptive water use - Wikipedia.
Decreasing block rate
A type of municipal water rate structure a community water system charges those it supplies; it decreases the per-unit price of water and increases water use. It’s sort of a bulk discount in water and is popular in areas that are rural or heavily industrial. Source: Understanding Your Water Bill | US EPA.
Drought rate
A type of municipal water rate structure charged by a community water system to those it supplies. Like seasonal rates, drought rates increase but instead of increasing seasonally, they rise when the water supply is stressed by drought. Higher prices during droughts are meant to incentivize water conservation and reduce water use. Source: Understanding Your Water Bill | US EPA.
Flat fee
A type of municipal water rate structure charged by a community water system to those it supplies. With a flat fee, the use cost, which is usually additional to the base service fee, is instead included in the base service fee. The price may differ by user group, such as residential, commercial, and agricultural, but does not vary with the amount of water used. This type of municipal rate structure is common in communities that do not meter water use. Source: Understanding Your Water Bill | US EPA.
Front Range Urban Corridor
Often shortened to just “Front Range” this refers to an oblong region with a population of more than five million, located along the eastern face of the Southern Rocky Mountains. It encompasses 18 counties in Colorado and Wyoming and is named after the mountain range that defines the corridor’s western boundary. Source: Front Range urban corridor - Wikipedia.
Gallons per household per day (GPHD)
A unit of water that measures the volume of water used by a household each day. Generally, this is calculated for a community water service, city, county, or state and reflects monthly volume of water used divided by the number of households in that community and divided by 30 days in an average month. This provides an average estimate of household water use and serves as a benchmark to measure changes in water use over time. GPHD is sometimes preferred to “per capita” or “per-person” units because water is typically purchased and used by entire households rather than by individuals.
Hundred Cubic Feet (HCF)
A volumetric unit used by community water systems to meter water use. One HCF is equivalent to about 748 gallons of water and is used interchangeably with Centum Cubic Feet (CCF). See also Centum Cubic Feet. Source: Understanding Your Water Bill | US EPA.
Increasing block rate
A type of municipal water rate structure charged by a community water system to those it supplies. The per-unit (1,000 Gallons; HCF; CCF) price of water increases as more water is used, units are typically grouped into blocks or tiers within increasing block rate structures (e.g., Block 1 = 0 to 7CCF $/CCF; Block 2 = 7 to 12 CCF $$/CCF; Block 3 = 12–18 CCF $$$/CCF). Increasing block rates promote water conservation and create water pricing that approaches the true marginal cost of the water supplied. Source: Understanding Your Water Bill | US EPA.
Indicator
A summary measure that provides information on the state of, or change in, the system being measured. Sometimes used interchangeably with metric, as in this report. See also Metric. Source: Fiksel et al. (2012).
Marginal price (cost)
In economics, this is change in the total price that arises when the quantity of something produced is incremented; the cost of producing an additional unit of some product. Said differently, the marginal cost is equal to the change in cost divided by the change in quantity. Source: Marginal cost - Wikipedia.
Metric
The measured value(s) used to assess specific indicators. It defines the units and how the indicator is being measured. Sometimes used interchangeably with indicator. Source: Fiksel et al., 2012.
Rate structure (municipal water)
The framework for pricing used by community water systems (CWS) to charge users of municipal water. Price structures commonly incorporate base rates or flat fees to cover capital costs and basic service and often include usage fees, which are charged based on customer use and may be segregated into tiers, depending on the volume of use.
Seasonal rate
A type of municipal water cost structure charged by a community water system to those it supplies; it varies from low-demand to high-demand seasons. Utilities may charge more per unit of water during the summer months when outdoor water use is highest, and less in the winter. Seasonal changes in price might be added to other rate structures (e.g., a seasonal increasing block rate). Source: Understanding Your Water Bill | US EPA.
Uniform rate
A type of municipal water cost structure charged by a community water system to those it supplies. With a uniform rate, the per-unit price is constant for all metered units of water consumed on a year-round basis. Still, metered service is required, and different user groups may be charged different rates. This type of rate structure provides revenue stability but is not designed to incur additional costs for wasteful or excessive water users. Source: Understanding Your Water Bill | US EPA.
Water budget–based rate
A type of municipal water cost structure the community charges its water users. Budget-based rates involve the utility or community water system calculating water budgets for households based on previous use patterns, lot or household size, or local precipitation conditions; users are charged one rate for being within the budget and a higher rate for water use that exceeds their utility-defined water budget. Source: Understanding Your Water Bill | US EPA.