Glossary/water dictionary

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abandoned water right

A water right that has not been put to beneficial use for generally five or more years, and in which the owner of the water right states that the water right will not be used or takes such actions that would prevent the water from being used beneficially.^

abandoned well

A well that is no longer used or a well removed from service; a well whose use has been permanently discontinued or is in a state of such disrepair that it cannot be used for its intended purpose. Generally, abandoned wells will be filled with concrete or cement grout to protect underground water from waste and contamination.^

absorption loss

The loss of water from infiltration or seepage into the soil during the process of priming, i.e. during the initial irrigation of a field; generally expressed as flow volume per unit of time.^

abutment (of a dam)

The part of a valley side wall against which a dam is constructed. An artificial abutment is sometimes constructed as a concrete gravity section to take the thrust of an arch dam where there is no suitable natural abutment.^

abutment seepage

Reservoir water that moves through seams or pores in the dam’s natural abutment material and exists as seepage.^

abyssal zone

The bottom of a deep ocean.^


The slow addition to land by deposition of water-borne sediment. An increase in land along the shores of a body of water.^


Gravity-driven waterways, similar in concept to a flume. Most are simple ditches with dirt banks, but they can be lined with concrete. They were important forms of irrigation in the development of agriculture in the American Southwest. The proliferation of cotton, pecans and green chiles as major agricultural staples owe their progress to the acequia system.^


(1) Chemicals that release hydrogen ions (H+ ) in solution and produce hydronium ions (H3O + ). Such solutions have a sour taste, neutralise bases, and conduct electricity. (2) Term applied to water with a pH of less than 7.0 on a pH scale of 0 to 14.^

acid aerosol

Airborne particles composed of sulphates (SOX), sulphuric acid (H2SO4 ), nitrates (NOX), and/or nitric acid (HNO3 ). Dry particle diameters are typically less than 1–2 microns.^

acid deposition

The introduction of acidic material to the ground or to surface waters. Involves a complex chemical and atmospheric phenomenon that occurs when emissions of sulphur and nitrogen compounds and other substances are transformed by chemical processes in the atmosphere, often far from the original sources, and then become deposited on the land or surface waters in either wet or dry forms. Wet deposition (commonly referred to as 'acid rain' or 'acid fog') results from precipitation such as rain, snow or fog. Dry deposition results from particle fallout or acidic gases.^

acid fog

Airborne water droplets containing sulphuric acid and/or nitric acid. Typical diameters are 3–30 microns.^

acid mine drainage (AMD)

Acidic water that flows into streams from abandoned mines or piles of mining waste or tailings. The acid arises from the oxidation of iron sulphide compounds in the mines by air, dissolved oxygen in the water, and chemoautotrophs, which are bacteria that can use the iron sulphide as an energy source. Iron sulphide oxidation products include sulphuric acid, the presence of which has reduced or eliminated aquatic life in many streams in mining regions^

acid neutralising capacity (ANC)

(1) A measure of the ability of water or soil to resist changes in pH. (2) The equivalent sum of all bases or base-producing materials, solutes plus particulates, in an aqueous system that can be titrated with acid to an equivalence point. The term designates titration of an “unfiltered” sample (formerly reported as alkalinity).^

acid precipitation

Atmospheric precipitation that is composed of the hydrolyzed by-products from oxidized halogen, nitrogen, and sulphur substances^

acid rain

Rainfall with a pH of less than 7.0. One of the principle sources is the combining of rain (H2O) and sulphur dioxide (SO2 ), nitrous oxides (NOx ), and carbon dioxide (CO2 ) emissions that are byproducts of the combustion of fossil fuels. These oxides react with the water to form sulphuric (H2SO4 ), nitric (HNO3 ) and carbonic acids (H2CO3 ). Long-term deposition of these acids is linked to adverse effects on aquatic organisms and plant life in areas with poor neutralising (buffering) capacity.^

acid soil (alkaline soil, neutral soil)

A description of one aspect of a soil’s chemical composition. Many plants will grow best within a range of pH rating from slightly acid to slightly alkaline. A pH rating of 7 means that the soil is neutral; a pH below 7 indicates acidity; a pH above 7 indicates alkalinity.^

acid-forming material

Material containing sulphide minerals or other materials, which if exposed to air, water, or weathering processes will form sulphuric acid.^


The condition of water or soil that contains a sufficient amount of acid substances to lower the pH below 7.0.^


Raising the acidity (lowering the pH) of a fluid by adding an acid. ^


A measure of how acid a solution may be. A solution with a pH of less than 7.0 is considered acidic. Solutions with a pH of less than 4.5 contain mineral acidity (due to strong inorganic acids), while a solution having a pH greater than 8.3 contains no acidity.^

activated carbon

A material produced by heating coal or wood in such a manner as to yield a porous structure, creating a very large internal surface area. Activated carbon is available in both powdered and granular forms, and is widely used to adsorb organic compounds from water and wastewater. It provides a means of removing tastes and odors from drinking water.^

activated carbon adsorption

The process of pollutants moving out of water and attaching on to activated carbon.^

activated sludge

The floc produced in raw or settled wastewater due to the growth of bacteria and other organisms in the presence of dissolved oxygen. It is the product that results when primary effluent is mixed with bacteria-laden sludge and then agitated and aerated to promote biological treatment, speeding the breakdown of organic matter in raw sewage undergoing secondary waste treatment.^

activated sludge process

A method of secondary wastewater treatment in which the waste is treated by micro-organisms in a well-aerated tank to degrade the organic material. A sedimentation tank is then used to remove the resultant sludge.^

active conservation storage

Storage of water for later release for purposes, such as municipal and industrial (M&I) uses, hydropower or irrigation.^

active solar water heater

A water heating system in which heat from the sun is absorbed by collectors and transferred by pumps to a storage unit. The heated fluid in the storage unit conveys its heat to the domestic hot water system of the house through a heat exchanger.^

active storage capacity

(1) The total amount of usable reservoir capacity available for seasonal or cyclic water storage. It is gross reservoir capacity minus inactive storage capacity. (2) More specifically, the volume of water in a reservoir below the maximum controllable level and above the minimum controllable level that can be released under gravity. In general, it is the volume of water between the outlet works and the spillway crest. In some instances, minimum pool operating constraints may prevent lowering the reservoir to the level of the outlet works, and the water below the minimum pool level is not considered to be in active storage.^


(1) The effective concentration of a chemical based on thermodynamic considerations. Activity and concentration have the same units and have the same value in very dilute solutions. (2) Adaptation Changes in an organism’s structure or habits that allow it to adjust to its surroundings.^

actual evapotranspiration

Represents a plant's actual rate of water uptake, which is determined by the level of available water in the soil.^

adaptive management

A process for implementing policy decisions as an ongoing activity that requires monitoring and adjustment. Adaptive management applies scientific principles and methods to improve resource management incrementally as managers learn from experience and as new scientific findings and social changes demand.^

adenosine triphosphate (ATP)

An organic, phosphate-rich compound important in the transfer of energy in organisms. Its central role in living cells makes it an excellent indicator of the presence of living material in water. A measure of ATP therefore provides a sensitive and rapid estimate of biomass. ATP is reported in micrograms per litre of the original water sample.^


Molecular attraction that holds the surfaces of two substances in contact, such as water and rock particles. Also, the attraction of water molecules to other materials as a result of hydrogen bonding.^

aline water

Water that contains significant amounts of dissolved solids. ^


Sometimes, water or soils contain an amount of alkali (strongly basic) substances sufficient to raise the pH value above 7.0 and thus be harmful to the growth of crops.^


Deposits of clay, silt, sand, gravel or other particulate material that has been deposited by a stream or other body of running water in a streambed, on a flood plain, on a delta, or at the base of a mountain.^

alternative technology

Technology that aims to use resources sparingly and to do minimum damage to the environment and its native species while permitting the greatest possible degree of control over the technology.^

appropriation doctrine

"A system for allocating water to private individuals used in most western (US) states. A system of 'prior appropriation' was in common use throughout the arid west when early settlers and miners began to develop the land. Prior appropriation is based on the concept of ""first in time, first in fight"". The first person to take a quantity of water and put it to 'beneficial use' has a higher priority of right than a subsequent user. Under drought conditions, higher priority users are satisfied before junior users receive water. Appropriative rights can be lost through non-use; they can also be sold or transferred apart from the land. This is in Contrast with riparian water rights."^


Farming of plants and animals that live in water, such as fish, shellfish, and algae.^


A pipe, conduit or channel designed to transport water from a remote source, usually by gravity.^


A water-bearing geologic formation. A geological formation or structure that stores and/or transmits water, such as to wells and springs. Use of the term is usually restricted to those water-bearing formations capable of yielding water in sufficient quantity to constitute a usable supply.^

aquifer (confined)

Soil or rock below the land surface that is saturated with water. There are layers of impermeable material both above and below it, and it is under pressure so that when the aquifer is penetrated by a well, the water will rise above the top of the aquifer.^

aquifer (unconfined)

An aquifer whose upper water surface (water table) is at atmospheric pressure, and thus is able to rise and fall.^

aquifer properties

The properties of an aquifer that determine its hydraulic behaviour and its response to abstraction.^

aquifer system

A body of permeable and relatively impermeable materials that functions regionally as a water-yielding unit. It comprises two or more permeable units separated, at least locally, by confining units (aquitards) that impede groundwater movement but do not greatly affect the regional hydraulic continuity of the system. The permeable materials can include both saturated and unsaturated sections.^

aquifer test

A test to determine hydrologic properties of an aquifer that involves the withdrawal of measured quantities of water from, or the addition of water to, a well and the measurement of resulting changes in the aquifer both during and after the period of discharge or addition (recharge).^

aquifer, saline / poor quality

An aquifer containing water that is high in total dissolved solids, and is unacceptable for use as drinking water.^

aquifer, sandstone

The type of aquifer supplying groundwater to large parts of the United States (e.g. upper Middle West, Appalachia, Texas). The water-bearing formation is often contained by shale strata, and the water has high levels of iron and magnesium^

aquifer, unconfined

An aquifer made up of loose material, such as sand or gravel, that has not undergone lithification (settling). In an unconfined aquifer the upper boundary is the top of the zone of saturation (water table).^

aquifer, volcanic Rock

An aquifer composed of rock that originated from a volcano, such as basalt. This type of rock may or may not be very permeable. Aquifuse: a formation that has no interconnected openings and hence cannot absorb or transmit water.^


A saturated but poorly permeable bed that impedes groundwater movement and does not yield water freely to wells, but which may transmit appreciable water to or from adjacent aquifers and, where sufficiently thick, may constitute an important groundwater storage unit. Aquitards are characterised by values of leakance that may range from relatively low to relatively high. Really extensive aquitards of relatively low leakance may function regionally as boundaries of aquifer flow systems.^

area (sub-area), hydrographic

Primarily these are sub-drainage systems, typically valleys, within a more comprehensive drainage basin. Hydrographic areas (valleys) may be further subdivided into hydrographic sub-areas based on unique hydrologic characteristics (e.g., differences in surface flows) within a given valley or area.^

area flooded

Area of a floodplain that is flooded in a specific stream reach, watershed or river basin; may be for a single flood event, but is usually expressed as an average, annual value based on the sum of areas from all individual flood events over a long period of time, such as 50 to 100 years, and adjusted to an average value.^

area of influence

The area surrounding a pumping or recharging well within which the water table or potentiometric surface has been changed due to the well’s pumping or recharge.^

area of origins protection

(1) Generally, laws, regulations, or policies that provide some form of protection to states, counties or regions from which an interbasin transfer of water is made. (2) US state and federal laws, dating back to 1931, enacted to guarantee that the counties that contribute water to state and federal water projects will get priority for water when it is needed to match future growth. As yet, these statutes have not received close legal scrutiny by the courts.^

area of review

The area around an underground injection well that may be influenced adversely by fluid injection. Typically, the extent of this area may be calculated by using the specific gravity and rate of introduction of the injected fluids, the size, storage capacity and hydraulic conductivity of the injection zone, and certain underground formation pressures.^

area-capacity curve

A graph showing the relation between the surface area of the water in a reservoir and the corresponding volume.^


A commonly used expression, generally synonymous with 'confined aquifer' and referring to subsurface (ground) bodies of water which, due to underground drainage from higher elevations and confining layers of soil material above and below the water body (referred to as an artesian aquifer), result in underground water at greater-than-atmospheric pressures.^

artesian aquifer

A commonly used expression, generally synonymous with (but a generally less favored term than) 'confined aquifer'. An artesian aquifer is an aquifer that is bounded above and below by formations of impermeable or relatively impermeable material. An aquifer in which groundwater is under pressure significantly greater than atmospheric and its upper limit is the bottom of a bed of distinctly lower hydraulic conductivity than that of the aquifer itself.^

artesian basin

A body of groundwater more or less compact, moving through soils with more or less resistance.^

artesian pressure

The pressure under which artesian water in an artesian aquifer is subjected, generally significantly greater than atmospheric pressure.^

artesian water

Groundwater that is under pressure when tapped by a well and is able to rise above the level at which it is first encountered. It may or may not flow out at ground level. The pressure in such an aquifer commonly is called artesian pressure, and the formation containing artesian water is an artesian aquifer or confined aquifer. ^

artesian well

1) A well bored down to the point, usually at great depth, at which the water pressure is so great that the water is forced out at the surface. The name is derived from the French region of Artois, where the oldest well in Europe was bored in 1126. (2) A well tapping a confined or artesian aquifer in which the static water level stands above the top of the aquifer. The term is sometimes used to include all wells tapping confined water. wells with water levels above the unconfined water table are said to have positive artesian head (pressure) and those with a water level below the unconfined water table (i.e. a 'negative artesian head'). If the water level in an artesian well stands above the land surface, the well is a 'flowing artesian well'. If the water level in the well stands above the water table, it indicates that the artesian water can and probably does discharge to the unconfined water body.^

artesian zone

A zone where water is confined in an aquifer under pressure so that the water will rise in the well casing or drilled hole above the bottom of the confining layer overlying the aquifer.^

artificial recharge (1)

(1) The addition of surface water to a groundwater reservoir by human activity, such as putting surface water into a spreading basin. (2) The designed replenishment of groundwater storage from surface water supplies, such as irrigation or induced infiltration from streams or wells. There are five common techniques to effect artificial recharge of a groundwater basin: [1] water Spreading, consisting of the basin method, stream-channel method, ditch method, and flooding method, all of which tend to divert surface water supplies to effect underground infiltration; [2] recharge pits designed to take advantage of permeable soil or rock formations; [3] recharge wells, which work directly opposite of pumping wells, although they generally have limited scope and are better used for deep, confined aquifers; [4] induced recharge, which results from pumping wells near surface supplies, thereby inducing higher discharge towards the well; and [5] wastewater disposal, which includes the use of secondary treatment wastewater in combination with spreading techniques, recharge pits, and recharge wells to reintroduce the water into deep aquifers thereby both increasing the available groundwater supply and also further improving the quality of the wastewater. ^

artificial recharge (2)

a process by which water is put back into groundwater storage from surface water supplies such as irrigation, or induced infiltration from streams or wells.^

artificial substrate

(1) A device placed in the water for a specified period of time that provides living spaces for a multiplicity of organisms; for example, glass slides, concrete blocks, multi-plate samplers, or rock baskets; used primarily to collect organisms in areas where the physical habitat is limiting or cannot be adequately sampled using conventional methods. (2) A device that is purposely placed in a stream or lake for colonisation of organisms. The artificial substrate simplifies the community structure by standardising the substrate from which each sample is taken. Examples of artificial substrates are basket samplers (made of wire cages filled with clean streamside rocks) and multiplate samplers (made of hardboard) for benthic organism collection, and plexiglass strips for periphyton collection.^

artificially developed water

Water that would not have reached a stream if left to flow in accordance with natural laws. If developed by an individual, that person may acquire rights to such waters superior to adjudicated rights of earlier appropriators of natural waters of the stream into which such waters are diverted.^


A mineral fibre that can pollute air or water and cause cancer or asbestosis when inhaled. The U.S. Environmental Protection Agency (EPA) has banned or severely restricted its use in manufacturing and construction.^


A disease associated with inhalation of asbestos fibres. The disease makes breathing progressively more difficult and can be fatal.^

attached ground water

The portion or amount of alkali substances in the ground sufficient to raise the pH value above 7.0 or to be harmful to the growth of crops, a condition called 'alkaline'.^

auxiliary spillway

A dam spillway built to carry runoff in excess of that carried by the principal spillway; a secondary spillway designed to operate only during exceptionally large floods. Also referred to as 'emergency spillway'. ^

available nutrients

Nutrient ions or compounds in forms that plants can absorb and utilise in growth.^

available soil water storage

Amount of water storable in the root zone at the time of irrigation.^

available water

The portion of water in a soil that can be absorbed by plant roots, usually considered to be that water held in the soil against a tension of up to approximately 15 atmospheres. ^

available water content (AWC)

A measure of the relative amount of water available in the upper levels of the soil strata that is available for use by plants.^

available water holding capacity

The capacity of a soil to hold water in a form available to plants. Also, the amount of moisture held in the soil between field capacity, or about one-third atmosphere of tension, and the wilting coefficient, or about 15 atmospheres of tension.^

average annual flood damages

The weighted average of all flood damages that would be expected to occur yearly under specified economic conditions and development. Such damages are computed on the basis of the expectancy in any one year of the amounts of damage that would result from floods throughout the full range of potential magnitude. ^

average annual recharge

The amount of water entering an aquifer on an average annual basis. In many, if not most, hydrologic conditions, 'average' has little significance for planning purposes because 'average' years might in fact be rare occurrences. ^

average annual runoff (yield)

The average water-year (Oct. 1 to Sept. 30) runoff or the supply of water produced by a given stream or water development project for a total period of record; measured in cubic feet per second or acre-feet.^

average conditions

The conditions under which a numerical value for a hydrologic variable, such as precipitation or streamflow, is equal to the arithmetic mean for a selected time period. ^

average discharge

In the annual series of the U.S. Geological Survey’s (USGS) reports on surface-water supply, the arithmetic average of all complete water years of record whether or not they are consecutive. The term 'average' is generally reserved for average of record, and 'mean' is used for averages of shorter periods, namely daily mean discharge.^

average water year

A term denoting the average annual hydrologic conditions based upon an extended or existing period of record. Because precipitation, runoff and other hydrologic variables vary from year to year, planners typically project future scenarios based on hydrologic conditions that generally include average, wet (high water), and drought (low water) years. ^

average year water demand

The demand for water under average hydrologic conditions for a defined level of development.^

average year water supply

The average annual supply of a water development system over a long period. For a dedicated natural flow, it is the long-term average natural flow for wild and scenic rivers, or it is 'environmental flows' as required for an average year under specific agreements, water rights, court decisions and congressional directives.^