PUBLICATION 442-758 A Glossary of Water-Related Terms Brian Benham, Assistant Professor and Extension Specialist, Department of Biological Systems Engineering, Virginia Tech The definitions and associated explanations of water-related terms presented here are intended to provide the reader with a working knowledge of terms that apply to Virginia’s water resources. The list is designed to assist the user in understanding and interpreting water related information that may come from sources as varied as governmental agencies, environmental groups, or the news media. While terms and definitions are fairly consistent, some termi- nology presented here could be defined differently to describe water resources issues in other locations. Advection – the process by which chemicals and heat A are transported along with the bulk motion of flowing Absorption –the process by which chemicals in gas- gas or liquid. For example, nitrate moves through soils eous, liquid or solid phases are incorporated into and and aquifer formations due predominantly to advection included within another gas, liquid, or solid chemical. (the bulk movement of water). For example, a sponge absorbs water. Algal bloom – large, visible masses of algae that develop in bodies of water during warm weather. Algal Acid mine drainage –water draining from areas blooms are the result of excessive levels of nutrients that have been mined for coal or other mineral ores. (generally phosphorus or nitrogen) in water. The drainage water is acidic, sometimes having a pH less than 2.0, because of its contact with sulfur-bearing – Anion – a negatively charged ion. Nitrate (NO3 ) and material. chloride (Cl–) are examples of anions. Acid rain – precipitation that has a low pH (here, low Anion exchange – the chemical process where nega- pH is defined as anything less than 5.6). The precipi- tive ions of one chemical are preferentially replaced by tation becomes acidic when moisture in the air reacts negative ions of another chemical. In water treatment, with sulfur and nitrogen pollutants in the atmosphere. the net effect is the removal of an unwanted ion from a water supply. For example, some water treatment facili- Acre-foot – the volume of water required to cover an ties or homeowners install an anion exchange system to area of one acre of land with 12 inches (1 foot) of water – remove nitrate (NO3 ) from their water supplies. depth. One acre-foot equals 325,851 gallons of water. Aquifer – a geologic formation that holds and yields Activated carbon – A material produced by heating usable amounts of water. The water in an aquifer is coal or wood in such a manner as to yield a porous struc- called groundwater. Aquifers may be categorized into ture, creating a very large internal surface area. Acti- confined aquifers and unconfined aquifers. vated carbon filters are widely used to adsorb organic compounds from water and wastewater and to remove Aquifer (confined) – an aquifer whose upper and tastes and odors from drinking water. lower, boundary is defined by a layer of natural material that does not transmit water readily. Water is “confined” Adsorption – the attachment of gas molecules, ions, under pressure similar to water in a pipeline. Drilling a or solutions to the surface of solids. For example, odors well into this type of aquifer is analogous to puncturing from freezers and refrigerators are adsorbed to baking a pressurized pipeline. In some areas confined aquifers soda. produce water without pumps (flowing artesian well). www.ext.vt.edu Produced by Communications and Marketing, College of Agriculture and Life Sciences, Virginia Polytechnic Institute and State University, 2009 Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Rick D. Rudd, Interim Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Alma C. Hobbs, Administrator, 1890 Extension Program, Virginia State, Petersburg. Aquifer (unconfined) – an aquifer whose upper pollution by fecal material and the presence of patho- boundary consists of a relatively porous material that genic bacteria that can cause diseases such as intestinal transmits water readily from the ground surface. The infections, dysentery, hepatitis, typhoid fever and chol- water level in an unconfined aquifer is the water table. era. Generally reported as colonies or colony forming units (cfu) per 100 milliliters (ml) of sample. (see fecal coliform) B Concentration – the amount of a given chemical or Bank – the margins of a stream or river channel. Banks pollutant in a particular volume or weight of air, water, are called right or left as viewed facing downstream, in soil, or other medium – often expressed as milligrams the direction of the flow. per liter (mg/l) or parts per million (ppm). Baseflow – that part of streamflow derived from Cone of depression – the lowering in groundwater groundwater flowing into a stream or river. levels around a well in response to groundwater with- drawal (the pumping of water). The extent of the cone Biosolids – an organic material resulting from the of depression defines the area of influence of a well. treatment of wastewater, often applied to the land as an amendment. In Virginia, land application of biosol- Consumptive use – the total amount of water taken ids or sewage sludge is regulated through the “Nutrient up by vegetation for transpiration and/or building of Management Program” administered by the Virginia plant tissue, plus any associated, unavoidable evapora- Department of Conservation and Recreation. tion of soil moisture. Brook – a natural stream of water, smaller than a river Contaminant – an undesirable substance not normally or creek; especially a small stream that breaks directly present, or an usually high concentration of a naturally- out of the ground, as from a spring or seep. occurring substance, in water, soil, or other environ- mental medium. In more restricted usage, a substance C in water that may be harmful to human health. Creek – small stream of water which serves as the Capillary fringe – a zone of partially saturated soil just natural drainage course for a drainage basin; a flowing above the water table. The depth of the fringe depends stream normally smaller than a river and larger than a upon the size and distribution of the pore spaces within brook. The term is often relative according to size and the soil media. locality. Cation – a positively charged ion. For example, cal- Cubic feet per second (cfs) – a rate of the flow. cium (Ca+2) and magnesium (Mg+2) are cations. One cfs is equal to a volume of water one foot deep Cation exchange – a process where positively and one foot wide flowing a distance of one foot in one charged ions of one chemical are preferentially replaced second. One cfs is equal to approximately 450 gallons by positive ions of another chemical. For example, per minute (gpm). water softeners replace Ca+2 and Mg+2 ions with sodium +2 (Na ) ions. D Channel (watercourse) – an open conduit either Depression storage – the volume of water con- naturally or artificially created that periodically or con- tained in natural depressions on the land surface, such tinuously contains moving water, or which forms a con- as puddles. necting link between two bodies of water. River, creek, stream, run, reach, branch, and tributary are some of the Diffusion – a process where chemicals or heat move terms used to describe natural channels. in response to differences in chemical concentration or temperature gradient. Movement is from high concen- Coliform bacteria – A group of nonpathogenic organ- tration (or temperature) to low concentration (or tem- isms (Colon bacilli) usually found in the digestive tract perature). This process could involve liquids, gases, of all warm-blooded animals and humans. The presence and solids. of coliform bacteria in water is an indicator of possible 2 Discharge area – an area or position where ground- water is delivered to the ground surface. Groundwater E can flow as springs or seeps, or contribute baseflow to Effluent – (1) something that flows out or forth, espe- streams or rivers. cially a stream flowing out of a body of water. (2) dis- charged wastewater such as the treated wastes from Discharge – the volume of water that passes a given animal production facilities, industrial facilities, or point during a given period. It is an all-inclusive out- wastewater treatment plants. flow term, describing a variety of flows such as from a pipe to a stream, or from a stream or river to a lake or Ephemeral stream – a stream that flows in response ocean. to runoff producing precipitation events and thus dis- continuing its flow during dry seasons. Such flow is Dispersion – the spreading and mixing of chemical usually of short duration. constituents in both surface and groundwaters caused by diffusion and mixing due to microscopic variations Estuarine waters – deepwater tidal habitats and in densities and velocities. tidal wetlands that are usually enclosed by land but have access to the ocean and are at least occasionally Distillation – the separation of different substances in diluted by freshwater runoff from the land (such as a solution by boiling off those of a lower boiling point bays, mouths of rivers, salt marshes). first. For example, water can be distilled and the steam condensed back into a liquid that is almost pure water. Erosion – the detachment and transport of soil par- Impurities remain in the concentrated residue. Distilla- ticles by water and wind. Sediment resulting from soil tion can be used to remove inorganic chemicals, some erosion represents the single largest source of nonpoint nonvolatile organic chemicals, and bacteria. source pollution in the United States.