Water Quality Glossary


Activated Carbon Filter: Wastewater or water treatment process to remove organics, taste, and odor.

Aerobic: in the presence of or requiring oxygen.

Alkalinity: capacity of water to neutralize acids by its content of bicarbonates, carbonates, or hydroxides.

Ambient Monitoring: performed to determine existing environmental conditions or contaminant levels in the environment, against which future conditions can be compared.

Anaerobic (Anoxic): in the absence of oxygen.

Assimilative Capacity: natural ability of a waterbody to neutralize or decompose potential pollutants without harmful effects to the environment.

Background Level: amount of a substance which occurs naturally in the environment.

Bacteria: microscopic one-celled organisms which live everywhere and perform a variety of functions. While decomposing organic matter in water, bacteria can greatly reduce the amount of oxygen in the water.

Best Management Practice (BMP): structural or managerial technique recognized as the most effective and practical means of controlling pollution from stormwater discharges.

Biochemical Oxygen Demand (BOD): measurement of the amount of oxygen consumed by microorganisms while decomposing organic matter in a product. BOD levels are indicative of the effect of the waste on fish or other aquatic life which require oxygen to live, and though not a specific compound, it is defined as a conventional pollutant under the federal Clean Water Act. Is a good indicator of the amount of organic waste that is readily consumed by bacteria.

Biodegradeable: capable of being broken down (decomposed) by microorganisms.

Chemical Oxygen Demand (COD): measurement of the amount of oxygen used in the chemical breakdown of organic mater in water. Is a good indicator of the total amount of organic waste.

Chlorination: addition of chlorine as a means of disinfecting drinking water or wastewater.

Coliform Bacteria: microorganisms which typically inhabit the intestines of warm-blooded animals. They are commonly measured in drinking water analyses to indicate pollution by human or animal waste.

Contaminant: any physical, chemical, biological, or radiological substance causing an impurity in the environment.

Discharge: flow of surface water in a stream or the flow of ground water from a spring or ditch.

Dissolved Oxygen (DO): oxygen dissolved in water and readily available to fish and other aquatic organisms.

Ecosystem: community of animals and plants and the physical environment in which they live.

Erosion: natural breakdown and movement of soil and rock by water, wind, or ice. The process may be accelerated by human activities.

Escherichia coli (E. coli): species of coliform bacteria that inhabit intestines of people and animals.

Estuary: a place where fresh and salt water mix, such as a bay, salt marsh, or where a river enters an ocean.

Hardness: characteristic of water which describes the presence of dissolved minerals.

Hazardous Waste: solid, liquid, or gaseous substance which, because of its source or measurable characteristics, is classified under state or federal law as potentially dangerous and is subject to special handling, shipping, and disposal requirements.

Heavy Metals: those metals (elements with high density, malleability, and electrical and thermal conductivity) that have high specific gravity and high atomic mass, such as lead, cadmium, zinc, copper, silver, and mercury.

Monitoring: Testing to detect and measure contaminants.

Nondischarge Systems: wastewater disposal systems that do not discharge to surface waters, such as spray irrigation, land application, or conventional septic systems.

Non-point Source (NPS) Contamination: water contamination derived from diffuse sources such as construction sites, agricultural fields, and urban runoff.

Non-point source discharges: discharges of contaminants that do not come from a single place such as an industrial site, or from a specific outlet such as a pipe. Some sources of non-point source discharge include runoff from agriculture, forestry and urban areas (for example stormwater and construction sites).

Non-point source (NPS) pollution: pollution discharged over a wide land area, not from one specific location. These are forms of diffuse pollution caused by sediment, nutrients, organic and toxic substances originating from land-use activities, which are carried to lakes and streams by surface runoff. Non-point source pollution is contamination that occurs when rainwater, snowmelt, or irrigation washes off plowed fields, city streets, or suburban backyards. As this runoff moves across the land surface, it picks up soil particles and pollutants, such as nutrients and pesticides.

Nuisance Contaminant: constituents in water which are not normally harmful to health but may cause offensive taste, odor, color, corrosion, foaming, or staining.

Nutrient: element essential for plant or animal growth. Major nutrients include nitrogen, phosphorus, carbon, oxygen, sulfur, and potassium.

Oil and grease: is a conventional pollutant defined in the Clean Water Act and is defined as any material recovered as a substance soluble in a solvent

Organic Compound: any carbon-based substance, including some petroleum products, solvents, pesticides, and halomethanes. Volatile organic compounds (VOCs) are those which are readily vaporized; a number of these are known or probable carcinogens.

Oxygen Demand: materials such as food waste and dead plant or animal tissue that use up dissolved oxygen in the water when they are degraded through chemical or biological processes. Chemical and biochemical oxygen demand (COD and BOD) are measures of the amount of oxygen consumed when a substance degrades.

Outfall: the place where a sewer, drain, or stream discharges; the outlet or structure through which reclaimed water or treated effluent is finally discharged to a receiving water body.

Pathogen: disease-causing biological agent such as a bacterium, virus, or fungus.

Pesticide: substance used for controlling, destroying, or repelling a specific pest. Includes fungicides, herbicides, insecticides, nematicides, rodenticides, defoliants, and plant growth regulators.

pH: numerical measure of acidity, with a scale of 0 to 14. Neutral is pH 7, values below 7 are acidic, and values above 7 are alkaline. pH is a measure of the acidity or alkalinity of water. A very high or very low pH means that water can be toxic for aquatic life. The pH range that is suitable for aquatic plants and animals is 6.5 to 9.

Point Source Contamination: water contamination from specific sources such as leaking underground storage tanks, landfills, industrial waste discharge points, or chemical mixing sites.

Point Source Discharges: discharges of contaminants that come from a stationary or fixed facility, for example from a pipe, ditch or drain.

Receiving Waters: bodies of water that receive runoff or wastewater discharges, such as rivers, streams, lakes, estuaries, and ground water.

Recharge: downward movement of water through soil to ground water.

Recharge Area: land area over which precipitation infiltrates into soil and percolates downward to replenish an aquifer.

Runoff: the portion of precipitation, snow melt, or irrigation which flows over and through soil, eventually reaching surface water (streams, rivers, lakes).

Salinity: quality of water based on its salt content; seawater contains approximately 18,000 parts per million of salt.

Sample: the water that is analyzed for the presence of EPA-regulated drinking water contaminants. Depending on the regulation, EPA requires water systems and states to take samples from source water, from water leaving the treatment facility, or from the taps of selected consumers.

Sanitary Survey: An on-site review of the water sources, facilities, equipment, operation, and maintenance of a public water systems for the purpose of evaluating the adequacy of the facilities for producing and distributing safe drinking water

Sediment: eroded soil and rock material, and plant debris, transported and deposited by water.

Settleable solids: is the term applied to the material settling out of suspension within a defined period. It may include floating material.

Solid Waste Management: related to storage, collection, transportation, treatment, utilization, processing, and final disposal of solid waste or resource recovery, and facilities necessary for such activities.

Solubility: amount of a substance that will dissolve in a given amount of another substance, typically water.

Turbidity: measure of water cloudiness due to suspended solids. Turbidity is a measure of the murkiness of water, reflecting the amount of sediment in the water. High turbidity reduces the amount of light available to the plants and animals living in the water. It reduces the ability of plants to photosynthesize. It also makes it difficult for fish and other animals to see their prey. Turbidity should be less than 5 NTU (turbidity measurement scale) for water to support plant growth.

Wastewater Treatment Plant (WWTP): facility that treats wastewater (and sometimes runoff) from domestic and/or industrial sources by a combination of physical, chemical, and biological processes.

Water Table: top of an unconfined aquifer, below which the pore spaces are saturated with water.

Watershed (Drainage Basin): all land and water that drains runoff to a stream or other surface water body.

Wetlands: areas that are regularly wet or flooded and have a water table that stands at or above the land surface for at least part of the year. Coastal wetlands extend back from estuaries and include salt marshes, tidal basins, marshes, and mangrove swamps. Inland freshwater wetlands consist of swamps, marshes, and bogs.