A - B - C - D - E - F - G - H - I - J K L - M - N - O - P - Q R - S - T - U - V - W- X Y Z


ACRE-FOOT - The volume of water required to cover one acre to a depth of one foot. Equal to 43,560 cubic feet or 325,851 gallons, or 1,233 cubic meters.

ADJUDICATION - Judicial process to determine the extent and priority of the rights of persons to use water in a river or aquifer system.

ALLUVIAL AQUIFER - An aquifer formed by material laid down by physical processes in a stream channel or on a floodplain.

ALLUVIAL PLAIN - A level, gently sloping, or slightly undulating land surface produced by extensive deposition of alluvium, usually adjacent to a stream that periodically overflows its banks.

ALLUVIUM - Unconsolidated clay, silt, sand, or gravel deposited during recent geologic time by running water in the bed of a stream or on its floodplain.

ANALYTICAL MODEL - Model that uses closed-form mathematical solutions to the governing equations applicable, for example, to ground-water flow and transport processes.

ANISOTROPY - Condition of having different properties in different directions.

APPROPRIATION - The right to use water for a beneficial use or the acquisition of such a right gained through the process of diverting water and putting it to a beneficial use.

APPROPRIATIVE RIGHTS - Appropriative water rights, generally found in western states, are created by diversion of water and putting it to beneficial use. Appropriative water rights have a priority based on the date of first usage. In times of shortage, junior appropriators are cut off while senior appropriators receive their full allotment.

AQUICLUDE - An impermeable layer of rock that does not allow water to move through it. Some shales, for example, have such low permeability that they effectively form an aquiclude.

AQUIFER - A saturated water-bearing formation, or group of formations, which yield water in sufficient quantity to be of consequence as a source of supply.

AQUIFER SYSTEM - Heterogeneous body of interbedded permeable and poorly permeable material that functions regionally as a water-yielding unit. It comprises two or more permeable beds separated at least locally by confining beds that impede vertical ground-water movement, but do not greatly affect the regional hydraulic continuity of the system; includes both saturated and unsaturated parts of permeable materials.

AQUIFER TEST—A test involving the withdrawal of measured quantities of water from, or addition of water to, a well (or wells) and the measurement of resulting changes in head in the aquifer both during and after the period of discharge or addition.

AQUIFER YIELD - Maximum rate of withdrawal that can be sustained by an aquifer. See YIELD.

AQUITARD - A part of a geologic formation (or one or more geologic formations) that is of much lower permeability than an aquifer and will not transmit water at a rate sufficient to feed a spring or for economic extraction by a well.

ARID—A climate characterized by dryness, variously defined as rainfall insufficient for plant life or for crops without irrigation; less than 10 inches of annual rainfall.

ARTESIAN AQUIFER - An aquifer in which ground water is confined under pressure significantly greater than atmospheric pressure. This pressure, called artesian pressure, is generally due to the weight of water at higher levels in the same zone and is sufficient to cause water to rise above the level of the aquifer in a well or natural fissure. An artesian aquifer is bounded above and below by confining beds of less permeable rock. Synonym: confined aquifer.

ARTESIAN WELL or ARTESIAN SPRING - A well or spring that taps ground water under pressure beneath an aquiclude so that water rises (though not necessarily to the surface) without pumping. If the water rises above the surface, it is known as a flowing artesian well.

ARTIFICIAL RECHARGE - Deliberate act of adding water to a ground-water aquifer by means of a recharge project. Artificial recharge can be accomplished via injection wells, spreading basins, or in-stream projects.

ATMOSPHERE - (1) The gaseous portion of the planet. (2) Standard unit of pressure representing the pressure exerted by a 29.92-inches (760-mm) column of mercury at sea level at 45 degrees latitude and equal to 14.696 pounds per square inch (psi) or 101.325 kilopascals (An).

AUGMENTATION PLAN—A court-approved plan that allows a water user to divert water out of priority so long as adequate replacement is made to the affected stream system and water right in quantities and at times so as to prevent injury to the water rights of other users.

AVAILABLE MOISTURE (OR MOISTURE) - Portion of water in a soil that can be absorbed by plant roots. It is the amount of water released from a wet soil between field capacity and the permanent wilting percentage.


BANK STORAGE - Change in storage in an aquifer resulting from a change in stage of an adjacent surface-water body.

BASEFLOW (OR BASE FLOW) - Stream flow derived mainly from ground-water seepage into the stream.


BASIN YIELD - Maximum rate of withdrawal that can be sustained by the complete hydrogeologic system in a basin without causing unacceptable declines in hydraulic head anywhere in the system or causing unacceptable changes to any other component of the hydrologic cycle in the basin. See YIELD.

BED - A layer of rock in the earth. Also the bottom of a body of water such as a river, lake, or sea.

BEDROCK - The solid rock that underlies any unconsolidated sediment or soil. Shale and granites are common types of bedrock in Colorado.

BENEFICIAL USE - Use of water, such as domestic, municipal, agricultural, mining, industrial, stockwatering, recreation, wildlife, artificial recharge, power generation, or contamination remediation, that provides a benefit. Water rights not put to beneficial use are subject to forfeiture. Historically, very few uses of water have been declared non-beneficial by courts.

BICARBONATE - The anionic constituent HCO3 that has a single negative charge as dissolved in water. Nearly all of the alkalinity in water is composed of bicarbonate. An alkalinity value (reported as mg/L CaCO3) for a water can be converted to the equivalent bicarbonate concentration in mg/L by multiplying by 1.219.


BRINE - Highly salty water, commonly with more than 10,000 milligrams per liter of chloride.


CALCITE - The mineral calcium carbonate (CaCO3). It is the main component of limestone.

CALCIUM - The element Ca that occurs as an ion with a double positive charge when dissolved in water; the major dissolved constituent constituting hardness in water.

CALCIUM-BICARBONATE TYPE - Freshwater that contains large concentrations of calcium (Ca) and bicarbonate (HCO3).

CALL—The request by an appropriator for water to which the person is entitled under his decree. Such a call will force those users with junior decrees to cease or diminish their diversions and pass the requested amount of water to the downstream senior making the call.

CAPILLARY FRINGE - Unsaturated zone immediately above the water table containing water in direct contact with the water table.

CAPTURE - Water withdrawn artificially from an aquifer derived from a decrease in storage in the aquifer, a reduction in the previous discharge from the aquifer, an increase in the recharge, or a combination of these changes. The decrease in discharge plus the increase in recharge is termed capture. Capture results in reduced surface flows.

CARBONATE - The anionic constituent CO3 that has two negative charges as dissolved in water or present in a mineral.

CERTIFICATION - The process whereby a permit to appropriate water is finalized based on the completion of the diversion work and past application of water to the proposed use in accordance with the approved water-right application. A certified water right has a legal, State-issued document that establishes a priority date, type of beneficial use, and the maximum amount of water that can be used annually.

CHLORIDE - The anionic form of the element chlorine (Cl) that has a single negative charge as dissolved in water.

CLASTIC ROCK—A consolidated sedimentary rock composed of broken fragments derived from pre-existing rocks and transported to their place of deposition; for example a sandstone, conglomerate, or shale.

CLAY - A very fine-grained material, smaller than silt (clay has a diameter of less than 1/256 mm). Clay is formed by the weathering and breaking down of rocks and minerals.

CLEAN WATER ACT—The federal law that establishes how the United States will restore and maintain the chemical, physical and biological integrity of the country’s water (oceans, lakes, streams and rivers, ground water and wetlands). The law provides protection for the country’s waters from both point and non-point sources of pollution.

COLIFORM—A bacteria that originates in the digestive system of mammals. If found in water, it alerts lab technicians that pathogens might be present.

COLLUVIUM (COLLUVIAL)—Loose rock and soil at the base of a cliff or steep slope, usually mixed and unsorted; distinguished from alluvium by not being deposited by running water in a stream.

COLORADO DOCTRINE—The doctrine regulating water usage by priority of appropriation as opposed to riparian rights

COLORADO WATER QUALITY CONTROL ACT—Legislation to prevent injury to beneficial uses made of state waters, to maximize the beneficial uses of water and to achieve the maximum practical degree of water quality in Colorado.

COMPACT—An agreement between states apportioning the water of a river basin to each of the signatory states. Approval by congress is required.

COMPACT CALL—The requirement that an upstream state cease or curtail diversions of water from the river system that is the subject of the compact to satisfy the downstream state’s compact entitlements.

COMMERCIAL WATER USE—Water for motels, hotels, restaurants, office buildings, other commercial facilities, and institutions. The water may be obtained from a public supply or may be self-supplied.

COMMUNITY WATER SYSTEM—A public system that serves a year-round residential population such as a group of homes receiving water from the same source.

CONDITIONAL WATER RIGHT—Legal preservation of a priority date that provides a water user time to develop a water right while reserving a more senior date. A conditional water right becomes an absolute right when water is actually put to beneficial use.

CONE OF DEPRESSION - A cone-shaped depression in the water table around a well or a group of wells. The cone is created by withdrawing ground water more quickly than it can be replaced.

CONFINED AQUIFER - An aquifer that is bounded above and below by confining layers. Because of the pressure created in a confined aquifer, the water level in a well drilled into a confined aquifer will rise above the top of the aquifer and, in some instances, above the land's surface.

CONFINING BED - A layer of relatively impermeable (i.e., incapable of transmitting fluids) material overlying an aquifer.

CONGLOMERATE - Rock that consists of non-sorted, cemented particles usually containing sand and gravel. Resembles concrete.

CONJUNCTIVE OPERATION OR USE - Coordinated use of surface and ground water supplies to meet demand so that both sources are used more efficiently.

CONSERVATION - Management of water resources to eliminate waste or maximize efficiency of use.

CONSERVATION STORAGE - Storage of water in a reservoir for later release for useful purposes such as municipal and industrial water supply, water quality, or irrigation.

CONSUMER CONFIDENCE REPORT—An annual water quality report prepared for the consumer by their supplier.

CONSUMPTIVE USE - That portion of water withdrawn from and lost to the immediate surface or ground-water storage environment. Typical withdrawals or uses include evaporation, transpiration, incorporation into products or crops, consumption by humans or livestock, or other removals.

CONTAMINANT—A substance not naturally occurring in water or occurring in an amount that presents a health risk.

CONTAMINANT PLUME - Zone of polluted ground water downgradient from a point source of pollution.

CONVEYANCE LOSS—Water that is lost in transit from a pipe, canal, conduit, or ditch by leakage or evaporation. Generally, the water is not available for further use; however, leakage from an irrigation ditch, for example, may percolate to a ground-water source and be available for further use.

CRYPTOSPORIDIUM and GIARDIA—Found in Colorado’s rivers and streams, cryptosporidium and giardia are microscopic organisms that, when ingested, can result in diarrhea, fever and other gastrointestinal symptoms.

CRYSTALLINE ROCK—An inexact but convenient term designating an igneous or metamorphic rock, as opposed to a sedimentary rock.

CUBIC FOOT PER SECOND (cfs) - Rate of discharge representing a volume of one cubic foot (28.317  10-3 m3) passing a given point during one second. This rate is equivalent to approximately 7.48 gallons (0.0283 m3) per second.


DARCY's EQUATION or LAW - Formula stating that the flow rate of water through a porous medium is proportional to the hydraulic gradient. The factor of proportionality is the hydraulic conductivity.

DECREE—An official document issued by the court defining the priority, amount, use, and location of the water right.

DEPLETION—Use of water in a manner that makes it no longer available to other users in the same system.

DEPLETION TIME - Time indicating how long it would take the watershed or the ground-water system to dry out if surface runoff or ground-water replenishment (recharge) were stopped from an instant onward, and if outflow was maintained at the rate it had at that instant. Depletion times of surficial waters usually are of the order of hours to weeks. They may run into months or years if the river basin includes large lakes. Depletion times of aquifers are usually of the order of tens to hundreds, and often thousands of years. As a consequence, rivers react quickly to precipitation and to the abstraction of water, whereas ground-water systems react very sluggishly to these events.

DEPTH TO WATER - The depth of the water table below the earth's surface.

DESIGNATED BASIN—An area in which the use of ground water is assumed not to impact the major surface river basin to which the designated basin would otherwise be tributary. Much of eastern Colorado is in designated basins.

DILIGENCE—Action taken towards the perfection of a conditional water right. In Colorado, when a conditional water right is granted by the court, the applicant must demonstrate the steps that have been taken toward perfecting that right. If diligence in perfecting an appropriation is not demonstrated, the right is lost.

DISCHARGE - The volume of water passing a particular point in a unit of time. Units of discharge commonly used include cubic feet per second (cfs) or gallons per minute (gpm)

DISCHARGE AREA - An area where ground water is lost naturally from an aquifer through springs, seeps, or hydraulic connection to other aquifers. The water leaving the aquifer is called discharge.

DISINFECTION BY-PRODUCTS—Chemicals, such as total trihalomethanes, formed from naturally occurring humic or fulvic acids and the disinfectant used in treating water

DISPERSION—The spreading and mixing of chemical constituents in ground water caused by diffusion and by mixing due to microscopic variations in velocities within and between pores.

DIVERSION - Physical removal of surface water from a channel. Also, the act of bringing water under control by means of a well, pump, or other device for delivery and distribution for a proposed use.

DIVISION ENGINEER—The person charged by delegation from the state engineer, Division of Water resources, Colorado Department of Natural Resources, with the duty of administering water flows and diversions within a specific water basin. Their offices are located in the cities where water courts are located.

DIVIDE (DRAINAGE DIVIDE)—Boundary between one drainage basin and another.

DOMESTIC WELL USE - Water used for drinking and other purposes by a household, such as from a rural well. Domestic use permits normally allow limited irrigation and outside watering uses.

DOWNGRADIENT - In reference to the movement of ground water, the "downstream" direction from a point of reference (e.g., a well).

DRAINAGE AREA - Area enclosed by a topographic divide from which direct surface runoff from precipitation normally drains by gravity into a stream above a specified location.

DRAINAGE BASIN - Hydrologic unit consisting of a part of the surface of the earth covered by a drainage system made up of a surface stream or body of impounded surface water plus all tributaries. The runoff in a drainage basin is distinct from that of adjacent areas. A river basin is similarly defined.

DRAWDOWN - Lowering of the ground-water surface or the piezometric pressure caused by pumping, measured as the difference between the original ground-water level and the current pumping level after a period of pumping.


EFFLUENT - Any substance, particularly a liquid, that enters the environment from a point source. Generally refers to wastewater from a sewage-treatment or industrial plant.

EPHEMERAL FLOW - When water flows in a channel only after precipitation.

EVAPORATION - Process of liquid water becoming water vapor, including vaporization from water surfaces, land surfaces, and snowfields, but not from leaf surfaces. Compare with transpiration.

EVAPOTRANSPIRATION - A collective term for water that moves into the atmosphere from evaporation from land or water and from transpiration from plants.


FIELD CAPACITY - Quantity of water held back by soil or rock against the pull of gravity. It is sometimes limited to a certain drainage period (2 or 3 days), thereby distinguishing it from specific retention, which is not limited by time.

FLOW—The volume of water moving past a point during a specified time. Also known as discharge.

FLOODPLAIN OR FLOOD PLAIN - Land bordering a stream, built up of sediments from overflow of the stream and subject to inundation when the stream is at flood stage.

FLUX - Refers to the rate of flow; it is the quantity of material or energy transferred through a system or a portion of a system in a unit time and is called mass flux. If the moving matter is a fluid, the flux may be measured as volume of fluid moving through a system in a unit time and is called volume flux. For most hydrologic applications, we desire to know the flux per unit area of a system rather than the flux of the entire system; the flux per unit area is called the flux density.

FLUME—A sloped channel that is utilized to convey water and is commonly constructed of wood or concrete. Some specialized flumes are used to measure flow (e.g. Parshall flume) by means of a calibrated throat or cross-section.

FRESHWATER - Water containing only small quantities (generally less than 1,000 milligrams per liter) of dissolved materials.


GAGING STATION - Site on a stream, lake, reservoir, or other body of water where direct systematic observations of hydrologic data are obtained.

GAINING STREAM - A stream that receives ground-water discharge from the zone of saturation.

GNEISS—A type of metamorphic rock that is foliated (lenticular or flaky texture), but less so than schist; formed by regional metamorphism.

GRAVEL PACK - Coarse sand and gravel placed in the annular space between the borehole and the well casing in the vicinity of the well screen. The purpose of the gravel pack is to minimize the entry of fine sediment into the well, stabilize the borehole, and allow the flow of ground water into the well.

GROUND WATER - Underground water that is generally found in the pore space of rocks or sediments and that can be collected with wells, tunnels, or drainage galleries, or that flows naturally to the earth's surface via seeps or springs.

GROUND WATER BASIN - Geologically and hydrologically defined area that contains one or more aquifers that store and transmit water and will yield significant quantities of water to wells.

GROUND WATER DIVIDE—A ridge in the water table or other potentiometric surface from which ground water moves away in both directions normal to the ridgeline.

GROUND WATER-FLOW MODEL - Application of a mathematical model to represent a site-specific ground-water-flow system.

GROUND WATER MINING - Pumping ground water from a basin at a rate that exceeds safe yield, thereby extracting ground water that had accumulated over a long period of time. See also overdraft.

GROUND WATER RESERVOIR—All rocks in the saturation zone.

GROUND WATER STORAGE - (1) Quantity of water in the saturated zone, or (2) water available only from the storage as opposed to capture.


HARDNESS - (1) Water-quality parameter that indicates the level of alkaline salts, principally calcium and magnesium, and expressed as equivalent calcium carbonate (CaCO3). Hard water is commonly recognized by the increased quantities of soap, detergent, or shampoo necessary to lather.

HEAD—The height above a standard datum of the surface of a column of water (or other liquid) that can be supported by the static pressure at a given point.

HEADGATE—A physical structure on a stream through which water is diverted into a ditch.

HETEROGENEOUS - Material is heterogeneous if its hydrologic properties differ anywhere. See also HOMOGENEOUS.

HOMOGENEOUS - Material is homogeneous if its hydrologic properties are identical everywhere.

HYDRAULIC CONDUCTIVITY - Factor of proportionality in Darcy's equation relating flow velocity to hydraulic gradient having units of length per unit of time. A property of the porous medium and the fluid (water content of the medium).

HYDRAULIC GRADIENT - Slope of the water table or potentiometric surface. The change is static head per unit of distance in a given direction. If not specified, the direction generally is understood to be that of the maximum rate of decrease in head.

HYDRAULIC HEAD or (STATIC) HEAD - Height that water in an aquifer can raise itself above an arbitrary reference level (or datum), generally measured in feet or meters. When a borehole is drilled into an aquifer, the level at which the water stands in the borehole (measured with reference to a horizontal datum such as sea level) is, for most purposes, the hydraulic head of water in the aquifer at that location. This term defines how much energy water possesses. Ground water possesses energy mainly by virtue of its elevation (elevation head) and of its pressure (pressure head). See also HYDROSTATIC HEAD. When ground water moves, some energy is dissipated and therefore a head loss occurs.

HYDRAULICALLY CONNECTED - A condition in which ground water moves easily between aquifers that are in direct contact. An indication of this condition is that the water levels in both aquifers are approximately equal.

HYDROGEOLOGY - The study of ground water and its relationship to geology. Also sometimes known as geohydrology.

HYDROGRAPH - Graph showing stage, flow, velocity, or other characteristics of water with respect to time. A stream hydrograph commonly shows rate of flow; a ground-water hydrograph shows water level or head.

HYDROLOGIC BUDGET OR BALANCE - Accounting of the inflow to, outflow from, and storage in a hydrologic unit such as a drainage basin, aquifer, soil zone, lake, or reservoir; the relationship between evaporation, precipitation, runoff, and the change in water storage, expressed by the hydrologic equation.

HYDROLOGIC CYCLE - The complete cycle that water can pass through, beginning as atmospheric water vapor, turning into precipitation and falling to the earth's surface, moving into aquifers or surface water, and then returning to the atmosphere via evapotranspiration.

HYDROLOGY - The study of the characteristics and occurrence of water, and the hydrologic cycle. Hydrology concerns the science of surface water and ground water, whereas hydrogeology principally focuses on ground water.


IGNEOUS ROCK—A rock or mineral that solidified from molten or partly molten material, i.e., from a magma. One of the three main classes into which all rocks are divided. Granite is a type of igneous rock.

IMPERVIOUS—Resistant to penetration by water or plant root.

INDUSTRIAL USES - Water used for a wide range of purposes by industries, including cooling water for electrical power generation, manufacturing, food preparation, washing of wastes, etc. The quality needed ranges substantially depending on the use.

INFILTRATION (SOIL) - Movement of water from the ground surface into the soil.

INJECTION WELL - Well used for injecting water or other fluid into a ground-water aquifer. See also ARTIFICIAL RECHARGE.

INORGANIC - Not made of or derived from living matter. Minerals are inorganic.

INSTREAM USE - Use of water that does not require withdrawal or diversion from its natural watercourse; for example, the use of water for navigation, recreation, and support of fish and wildlife.

INTERBASIN TRANSFER - Physical transfer of water from one watershed to another.

INTERMITTENT FLOW - Surface water flowing only during periods of seasonal runoff.

INTRINSIC PERMEABILITY - Quantitative measure of fluid-transmitting ability of a porous medium that is related to the size and interconnectedness of the void openings. See also PERMEABILITY.

IRRIGATION DISTRICT—A legal entity, with definite geographic boundaries, created by statute in order to develop large irrigation projects

IRRIGATION USE - Water applied to the soil surface by center pivots, ditches, or other means or to the soil subsurface by tubes to add to the water available for plant growth.

ISOTROPIC - Said of a medium whose properties are the same in all directions. See also ANISTROPY.

J - K - L

JUNIOR APPROPRIATOR RIGHT - Holder of a surface- or ground-water right that was acquired subsequent to other water rights on the same stream or aquifer.


KARST - A terrain or type of topography generally underlain by soluble rocks, such as limestone, gypsum, and dolomite, in which the topography is chiefly formed by dissolving the rock; karst is characterized by sinkholes, depressions, caves, and underground drainage.


LACUSTRINE - Pertaining to or formed in a lake or lakes.

LIMESTONE - Composed mainly of calcium carbonate (CaCO3). Like most of the rocks found at the surface in the state, it is a sedimentary rock.

LITHOLOGY - (1) The description of rocks on the basis of physical characteristics, such as color and mineral composition. (2) The physical character of a rock.

LIVESTOCK WATER USE—Water for livestock watering, feed lots, dairy operations, fish farming, and other on-farm needs. Livestock as used here includes cattle, sheep, goats, hogs, and poultry.

LOESS - Non-stratified sediment composed of silt-sized particles deposited by the wind.

LOSING STREAM - A stream that contributes water to the zone of saturation, recharging the ground water.


MAJOR DISSOLVED CONSTITUENTS - The largest dissolved constituents in water are calcium, magnesium, sodium, bicarbonate, chloride, sulfate, and silica, although nitrate can sometimes be a major constituent.

MARINE - Relating to the sea. Native to or formed by the sea.

MAXIMUM CONTAMINANT LEVEL (MCL) - Maximum level of a contaminant allowed in water by Federal law. Based on health effects and currently available treatment methods.

METAMORPHIC ROCKS— Any rock that has recrystallized due to heat, pressure, or chemical environment at depth in the Earth’s crust. All metamorphic rocks are derived from pre-existing rocks. This is one of the three main classes into which all rocks are divided. Schist, gneiss, slate, and marble are types of metamorphic rocks.

MGD—Million gallons per day. A measure of flow rate.

MILLIGRAMS PER LITER (mg/L) - Milligrams of a substance dissolved in one liter of water. The value is essentially the same as a part per million in freshwater because one liter of distilled water weighs one million milligrams (one kilogram). This measure is equivalent to parts per million (ppm).

MINIMUM STREAMFLOW REQUIREMENT—Water right decreed to the Colorado Water Conservation Board requiring that a set amount of water be maintained in a watercourse for the purpose of reasonably maintaining the environment. The minimum stream flow right takes its place in the appropriation system in the manner of another junior water right, although diversion of the water is not required.

MINING WATER USE—Water use for the extraction of minerals occurring naturally including solids, such as coal and ores; liquids, such as crude petroleum; and gases, such as natural gas. Also includes uses associated with quarrying, well operations, milling, and other preparations customarily done at the mine site or as part of a mining activity.

MONITORING WELL - Non-pumping well used primarily for taking water-quality samples and measuring ground-water levels. Also see OBSERVATION WELL.


NONCOMMUNITY WATER SYSTEM—A public water system that serves a year round nonresidential population such as schools and businesses.

NONCONSUMPTIVE USE —Use that leaves the water available for other uses. Examples are hydroelectric power generation and recreational uses.

NONPOINT SOURCE - Source of water pollution that originates from a broad area, such as agricultural chemicals applied to fields or acid rain.

NON-POTABLE—Water not suitable for drinking.

NONTRIBUTARY GROUND WATER—Underground water in an aquifer that neither draws from nor contributes to a natural surface stream in any measurable degree.

NOT NONTRIBUTARY GROUND WATER—Groundwater that is hydrologically connected to a surface stream system.

NPDES PERMIT - Permit issued under the National Pollutant Discharge Elimination System for companies or other entities discharging pollutants directly into the waters of the United States.


OBSERVATION WELL - Non-pumping well used primarily for observing the elevation of the water table or the piezometric pressure; also to obtain water-quality samples. Also see MONITORING WELL.

ORGANIC—Pertaining to or relating to a compound containing carbon. For example, petroleum products contain organic compounds derived from plant and animal remains.

OVERDRAFT - (1) Pumping of ground water for consumptive use in excess of safe yield; (2) the condition of a ground-water basin where the amount of water withdrawn exceeds the amount of water captured over the basin over a period of time. The use of water in excess of the perennial yield.


PARTS PER BILLION (ppb) - Micrograms per liter; one-one thousandth of milligrams per liter.


PERCHED WATER TABLE - Water table of a relatively small ground-water body lying above the general water table, and separated from the underlying aquifer by an aquiclude.

PERCOLATION - Laminar-gravity flow through unsaturated and saturated earth material.

PERENNIAL FLOW - Year-round flow.

PERMEABILITY - (1) Ability of a material (generally an earth material) to transmit fluids (water) through its pores when subjected to pressure or a difference in head. Expressed in units of volume of fluid (water) per unit time per cross section area of material for a given hydraulic head; (2) description of the ease with which a fluid may move through a porous medium; abbreviation of intrinsic permeability. It is a property of the porous medium only, in contrast to hydraulic conductivity, which is a property of both the porous medium and the fluid content of the medium.

pH - Measure of the relative acidity or alkalinity of water. Defined as the negative log (base 10) of the hydrogen ion concentration. Water with a pH of 7 is neutral; lower pH levels indicate an increasing acidity, while pH levels above 7 indicate increasingly basic solutions.

PHREATIC - Indicating the water-saturated zone below the water table. The phreatic zone is the area of the subsurface that is saturated with water.

PHREATIC ZONE - Same as zone of (ground-water) saturation. Was originally used to designate water in the upper part of the zone of saturation.

PHREATOPHYTE - Plant whose roots generally extends downward to the water table and customarily feed on the capillary fringe. Phreatophytes are common in riparian habitats. Term literally means “well” plant or water-loving plant. Common examples in Colorado are cottonwoods and willows.

POINT SOURCE - Source of pollution that originates from a single point, such as an outflow pipe from a factory.

POLLUTION—Contamination from human activities that restricts the uses of water.

POROSITY - Fraction of bulk volume of a material consisting of pore space. Porosity determines the capacity of a rock formation to absorb and store ground water.

POROUS - Geologically, this term describes rock that permits movement of fluids through small, often microscopic openings, much as water moving through a sponge. Porous rocks may contain gas, oil, or water.

POTABLE—Water that does not contain pollution, contamination, objectionable minerals or infective agents and is considered safe for domestic consumption; drinkable.

POTENTIOMETRIC SURFACE - Imaginary surface representing the static head of ground water and defined by the level to which water will rise in a well. The water table is a particular potentiometric surface.

PRECIPITATION - Water in some form that falls from the atmosphere. It can be in the form of liquid (rain or drizzle) or solid (snow, hail, sleet).

PRIOR APPROPRIATION - Doctrine for prioritizing water rights based upon dates of appropriation (“first in time, first in right”). Common method for allocating water rights in the western United States.

PRIORITY—Seniority date of a water right or conditional water right to determine their relative standing to other water rights and conditional water rights deriving water from a common source. Priority is a function of both the appropriation date and the relevant adjudication date of the right.

PRIORITY DATE—The date a water right is established.

PUBLIC SUPPLY - Water used for drinking and other purposes supplied to many people by a system operated by a city, housing unit, industry, etc.

PUBLICLY OWNED TREATMENT WORKS (POTW)-Public treatment plant that provides water for a variety of uses, such as commercial water, domestic water, thermoelectric power water, industrial water, and public water.

Q - R

RAW WATER—Untreated water.

RECHARGE - The replenishment of ground water in an aquifer. It can be either natural, through the movement of precipitation into an aquifer, or artificial in the pumping of water into an aquifer.

RECHARGE AREA - A geographic area where water enters (recharges) an aquifer. Recharge areas usually coincide with topographically elevated regions where aquifer units crop out at the surface. In these areas infiltrated precipitation is the primary source of recharge. The recharge area also may coincide with the area of hydraulic connection where one aquifer receives flow from another adjacent aquifer.

RECLAIMED WASTEWATER—Wastewater treatment plant effluent that has been diverted for beneficial use before it reaches a natural waterway or aquifer.

RECYCLED WATER—Water that is used more than one time before it passes back into the natural hydrologic system.

RESERVOIR CAPACITY - Amount of water a surface reservoir is capable of storing.

RETURN FLOW - Part of water that is not consumed and returns to its source or another body of water.

RIPARIAN - Of, or pertaining to, rivers and their banks.

RIPARIAN HABITAT - Natural home of plants and animals occurring in a thin strip of land bordering a stream, river, or adjoining water body. Dominant vegetation often consists of phreatophytes.

RIPARIAN RIGHTS - Surface-water rights assigned on the basis of land ownership along a stream reach.

RISK ASSESSMENT - Evaluation of the potential for exposure to contaminants and the associated hazard.

RUNOFF - Drainage or flood discharge that leaves an area as surface flow or as pipeline flow, having reached a channel or pipeline by either surface or subsurface routes. Generally, surface water entering river, lakes, or reservoirs.


SAFE DRINKING WATER ACT (SDWA)—Federal legislation passed in 1974 that regulates the treatment of water for human consumption and requires testing for and elimination of contaminants that might be present in the water.

SAFE YIELD - (1) Rate of surface-water diversion or ground-water extraction from a basin for consumptive use over an indefinite period of time that can be maintained without producing negative effects; (2) the annual extraction from a ground-water unit which will not, or does not, produce a negatitive effect, (3) the attainment and maintenance of a long-term balance between the amount of ground water withdrawn annually and the annual amount of recharge; (4) the maximum quantity of water that can be guaranteed from a reservoir during a critical dry period.

SALINE WATER - Water containing more than 10,000 parts per million (ppm) of dissolved solids of any type. Brackish water contains between 1,000 and 10,000 ppm of dissolved solids.

SALINITY - The total quantity of dissolved salts in water, usually measured by weight in milligrams per liter (mg/L) or parts per million (ppm). The upper limit for freshwater is 1,000 mg/L; natural seawater has a salinity of approximately 35,000 mg/L.

SAND - A rock fragment or mineral particle smaller than a granule and larger than a coarse silt grain. Its diameter ranges from 1/16 to 2 mm.

SANDSTONE - Rock formed by the compaction and/or cementing of sand. Cement (matrix) material can be calcite, hematite (FeO2), or other materials.

SATURATED THICKNESS - The vertical thickness of an aquifer that is full of water. The upper surface is the water table. The height of the hydrogeologically defined aquifer unit in which the pore spaces are filled (saturated) with water. For the High Plains aquifer and similar unconfined, unconsolidated aquifers, the saturated thickness is equal to the difference in elevation between the bedrock surface and the water table. The predevelopment saturated thickness is based on the best available estimate of the elevation of the water table prior to human alteration by ground water pumping.

SATURATED ZONE—A Subsurface zone in which all the interstices are filled with water under pressure greater than atmospheric. The upper surface of the saturation zone is the water table.

SCHIST— A type of metamorphic rock that is strongly foliated (having lenticular or flaky texture). Schists can be readily split into thin flakes or slabs.

SECONDARY STANDARD - The maximum concentration recommended for a substance in water for a particular use. An example of secondary standard for drinking water is 250 mg/L chloride that is based mainly on taste.

SEDIMENT - Rock or other material that has been worn or broken into small pieces. Sediment is often carried from its original location by wind or water and deposited in other areas.

SEDIMENTARY ROCK—A rock resulting from the consolidation of loose sediment that has accumulated in layers. One of the three main classes into which all rocks are divided. Sandstone, shale, and limestone are types of sedimentary rock.

SEEP - A discharge of water that "oozes out of the soil or rock over a certain area without distinct trickles or rivulets" (from H. Bouwer, 1978, Groundwater Hydrology: New York, McGraw - Hill, 480 p.).

SEMIARID - Said of a type of climate in which there is slightly more precipitation (10 - 20 inches [254 - 508 mm]) than in an arid climate, and in which sparse grasses are the characteristic vegetation.

SENIOR APPROPRIATOR - Owner of a surface-water right whose right was acquired prior to other rights holders on the same stream.

SHALE - Rock that is often impervious to water (will not allow water to move through it) but rather soft, brittle, and easily eroded. Shale is the result of compaction of silt or mud. Much of the Permian and Pennsylvanian strata in Colorado consists of various shales, often brightly colored.

SILT - A rock fragment or mineral particle with a diameter of 1/16 mm to 1/256 mm, smaller than a very fine sand grain and larger than coarse clay.

SINK (SINKHOLE) - A depression in the surface of the earth caused by solution and/or collapse of rock. A sink is an entry point for water into cave and spring systems. All sinks will carry water into the subsurface.

SODIUM - The cationic form of the element sodium (Na) that has a single positive charge as dissolved in water.

SODIUM CHLORIDE TYPE - Water in which the constituents with the largest dissolved concentrations are sodium (Na) and chloride (Cl). Sodium chloride type water is usually derived from dissolution of rock salt (the mineral halite with the composition NaCl).

SODIUM SULFATE TYPE - Water in which the constituents with the largest dissolved concentrations are sodium (Na) and sulfate (SO4). Calcium usually is present in substantial concentrations in this type of water, but the calcium is limited from being at higher levels due to the solubility limits of minerals such as calcite (CaCO3) and gypsum (CaSO4.2H2O).

SOIL MOISTURE - Water in the root zone.

SOLUTION - Geologically, the action of the dissolving of rock by water or the term to describe the water that dissolves the rock. Limestone dissolves in acidic solutions; gypsum can be dissolved in pure water. On dissolving the rock, the water becomes a calcite solution (the calcite may later be redeposited).

SPECIFIC CONDUCTANCE - Measure of the ability of water to conduct an electrical current, expressed in micromhos per centimeter at 250C. Specific conductance is related to the type and concentration of ions in solution and can be used for approximating the dissolved-solids content of the water.

SPECIFIC DISCHARGE - For ground water, the rate of discharge of ground water per unit area measured at right angles to the direction of flow.

SPECIFIC RETENTION - Ratio of the volume of water that a given body of rock or soil will hold against the pull of gravity to the volume of the body itself. It is usually expressed as a percentage. Compare with field capacity.

SPECIFIC STORAGE - Volume of water released from or taken into storage per unit volume of the porous medium per unit change in head. It is the three-dimensional equivalent of storage coefficient or storativity, and is equal to storativity divided by aquifer saturated thickness.

SPECIFIC YIELD - The volume of water that can be drained by gravity from the pores of sand, gravel, soil, or rock divided by the total volume of material and expressed as a percent.
SPRING - A place where ground water flows naturally from the earth into a body of surface water or onto the land surface, at a rate sufficient to form a current.

STAGE - Elevation of stream surface above a defined datum, usually mean sea level.

STATE ENGINEER—The person charged by state law with the supervision and administration of water and the enforcement of decreed priority and legislative enactments. The State Engineer discharges the obligations of the state of Colorado imposed by compact or judicial orders and coordinates the work of the division of water resources with other departments of state government. The State Engineer has rule-making obligations and supervisory control over measurements, record keeping, and distribution of the public water of the state and all employees under his direction and any other such acts as may be reasonable necessary to enable the performance of his duties.

STORATIVITY or STORAGE COEFFICIENT - Volume of water released per unit area of aquifer and per unit drop in head. Storage coefficient is a function of the compressive qualities of water and matrix structures of the porous material. A confined aquifer's ability to store water is measured by its storage coefficient. Storativity is a more general term encompassing both or either storage coefficient and/or specific yield.

STREAM REACH - Specific portion of the length of a stream.

STREAMFLOW - Discharge that occurs in a natural channel. A more general term than runoff, streamflow may be applied to discharge whether or not it is affected by diversion or regulation.

SULFATE - The anionic constituent SO4 that has two negative charges as dissolved in water.

SURFACE WATER - Water found at the earth's surface, usually in streams or lakes.


TERRACES - In geologic terms, these are flat broad benches of land that lie above the immediate floodplain of a stream. Terraces represent a prior floodplain level of the stream.

THERMAL POLLUTION - Reduction in water quality caused by increasing its temperature, often due to the disposal of waste heat from industrial or power generation processes. Thermally polluted water often undergoes biological changes that render it less valuable for drinking, recreation, habitat, or industrial use.

TOTAL DISSOLVED SOLIDS (TDS) - The total quantity of minerals (salts) in water, usually measured by weight in milligrams per liter (mg/L) or parts per million (ppm).

TRANSMISSIVITY - Flow capacity of an aquifer measured in volume per unit time per unit width. Equal to the product of hydraulic conductivity times the saturated thickness of the aquifer.

TRANSPIRATION - Vaporization of water given off by plants.

TREATED WATER—Water that has been filtered and disinfected.

TRIBUTARY—A tributary is generally regarded as a surface water drainage system which is interconnected with a river system. Under Colorado law, all surface and groundwater, the withdrawals of which would affect the rate or direction of flow of a surface stream within 100 years, is considered to be tributary to a natural stream.


UNCONFINED AQUIFER - An aquifer that is not bounded above by an aquitard; water levels in wells screened in an unconfined aquifer coincide with the elevation of the water table.

UNCONFORMITY - Contact between rock layers representing a break or interruption in the deposition process, which creates a gap in the geologic record.

UNDERFLOW - (1) Ground-water flow within a streambed below a surface stream; (2) lateral movement of water through the soil zone, also known as interflow.

UNSATURATED ZONE - Also known as the vadose zone, this is the area of soil or rock just above the water table.

UPGRADIENT - In reference to the movement of ground water, the "upstream" direction from a point of reference (e.g., a well).


VADOSE ZONE - Unsaturated (not completely filled with water) zone lying between the earth's surface and the top of the ground water. Also known as unsaturated zone and zone of aeration.

VOID - Pore space or other openings in rock. The openings can be very small to cave-size and are filled with water below the water table.

VOLATILE ORGANIC COMPOUND (VOC) - Organic chemical that evaporates relatively easily when exposed to air.


WASTEWATER—Water that carries wastes from homes, businesses, and industries.

WATER BALANCE - A mathematical construction that shows the amount of water leaving and entering a given watershed or aquifer.

WATER COURT—A specific district court that has exclusive jurisdiction to hear and adjudicate water matters. There are seven water courts in Colorado, a judge, who is also a district court judge, presides over each court.

WATER DEMAND - Amount of water used over a period of time.

WATER FLUX - A volume of water per unit area per time.

WATER QUALITY - Physical, chemical, and biological characteristics of water and how they relate to it for a particular use.

WATER QUALITY CONTROL ACT—Colorado statute enacted in 1981 to protect, maintain, and improve the quality of state waters through prevention, abatement, and control of water pollution. This act created the nine member Water Quality Control Commission who are responsible for developing specific water quality policy.
WATER RIGHT - Any vested or appropriation right under which a person may lawfully divert and use water. It is a real property right appurtenant to and severable from the land on or in connection with which the water is used. Water rights pass as an appurtenance with a conveyance of the land by deed, lease, mortgage, will, or inheritance.

WATERSHED - An area from which water drains and contributes to a given point on a stream or river.

WATER TABLE - A fluctuating demarcation line between the unsaturated (vadose) zone and the saturated (phreatic) zone that forms an aquifer. It may rise or fall depending on precipitation (rainfall) trends. The water table is semi-parallel to the land surface above but is not always a consistent straight line. Because of impervious beds of shale, etc., local water tables can be perched above the area's average water table.

WATER TRANSFER - Legal change in a water right reflecting some combination of a conveyance of ownership of diversion, place of use, and/or type of use to another.

WATER VAPOR - Water present in the atmosphere in gaseous form; the source of all forms of condensation and precipitation. Water vapor, clouds, and carbon dioxide are the main atmospheric components in the exchange of terrestrial radiation in the troposphere serving as a regulator of planetary temperatures via the greenhouse effect.

WATER YEAR - Twelve-month period in which the U.S. Geological Survey reports surface-water supplies. Water years begin October 1 and end the following September 30, and are designated by the calendar year in which the water year ends.

WEIR—A vertical structure in an open channel with a calibrated opening that measures water’s rate of flow. (see flume)

WELL - A vertical excavation into an underground rock formation.

WELL PERMIT—The granting of permission by the State Engineer allowing the digging of a hole in search of groundwater to apply to a benificial use. A written permit obtained by the state stating permission to dig a hole to find groundwater.

WELL SCREEN - A slotted section of pipe usually placed in the borehole adjacent to the main aquifer unit or units that supplies the well with water.

WELL YIELD - Pumping rate that can be supplied by a well without drawing the water level in the well below the pump intake. See YIELD.

WETLAND - Land with a wet spongy soil, where the water table is at or above the land surface for at least part of the year.


YIELD - Amount of water that can be supplied from a reservoir, aquifer, basin, or other system during a specified interval of time. This time period may vary from a day to several years depending upon the size of the system involved.



• Denver Water Community Relations Office Denver Water Glossary of Frequently Used Water Terms,: Denver, Colorado 24 p.
• Estimated Use of Water in the United States in 1990, USGS: (7/30/2001)
• Jackson, J.A., editor, 1997, Glossary of Geology (Fourth Edition): Alexandria, Virginia, American Geological Institute, 769 p.
• Moore, J.E., Zaporozec,A, and Mercer, JW, 1996, Groundwater: A Primer: Alexandria, Virginia, American Geological Institute, 53 p.
• Schloss, J.A., Buddemeier, R.W., and Wilson, B.B., 2000, An Atlas of the Kansas High Plains Aquifer: Kansas Geological Survey, Educational Series 14, 92p
• Water Information Program, Definition of Water Terms, (2/14/97)