Water Quality Glossary

Water Quality Glossary

Water quality is a term that describes the condition of the body of water, based on a number of factors. The quality of the water is usually evaluated based on its intended usage; is the specific water to be used for drinking, irrigating or washing cars, for example? The chemical, physical and biological characteristics measured to determine water quality can include:

  • the concentration of dissolved oxygen
  • bacteria levels
  • the amount of salt (or salinity)
  • the amount of material suspended in the water (turbidity)
  • the concentration of microscopic algae
  • quantities of pesticides, herbicides, heavy metals, and other contaminants

Alluvial – Particles or sediment within running water that are deposited when the water flow decreases.

Ambient – Natural conditions in the surrounding environment which may affect water quality in addition to the source pollution or source of contamination.

Assimilative capacity – The amount of pollution a water body can receive without noticeably affecting quality; this is governed by the natural ability of the water to dilute or transform contaminants.

Beneficial use – Water utilized for an accepted man-made use such as municipal water supply, industry, irrigation, mining, hydroelectric power, navigation, recreation, livestock raising, aesthetics, and aquatic life and wildlife

Biochemical oxygen demand (BOD) – The amount of oxygen that bacteria will consume while decomposing organic matter in a sealed sample without the presence of oxygen. The main focus of wastewater treatment plants is to reduce the BOD in the effluent discharged to natural waters.

Biochemical oxygen demand (BOD) Levels – Most pristine rivers will have a BOD below 1 mg/L. Moderately polluted rivers may have a BOD value in the range of 2 to 8 mg/L. Municipal sewage that is efficiently treated by a three-stage waste water treatment process would have a value of about 20 mg/L or less. Untreated sewage varies, but averages around 200 mg/L in the United States.

Brackish – Water that is more salty than fresh water but with less salinity than saltwater. Brackish water is usually found in estuaries where the amount of salinity is constantly fluctuating, like Mobile Bay.

Effluent – The out-flow water or waste water from any water processing system or device. Alternatively, effluent is the general term in waste water treatment for the final water which is discharged from a treatment plant, usually into a natural water source, after complete treatment to meet current effluent water quality standards. Effluent water is also often recycled as irrigation water for golf courses and some agricultural applications.

Non-point Source Pollution, NPS – Pollution not from one specific location. Non-point source pollution is caused by rainfall or snowmelt moving over and through the ground. As the runoff moves, it picks up and carries away natural and human-made pollutants, finally depositing them into lakes, rivers, wetlands, coastal waters and ground waters. It can include:

  • excess fertilizers, herbicides and insecticides from agricultural lands and residential areas
  • oil, grease and toxic chemicals from urban runoff and energy production
  • sediment from improperly managed construction sites, crop and forest lands, and eroding stream banks
  • salt from irrigation practices and acid drainage from abandoned mines
  • bacteria and nutrient pollution from livestock, pet wastes and faulty septic systems
  • Nutrient pollution – Pollution caused by fertilizers, yard debris, animal waste, stormwater runoff, sewage discharges and overflows.
  • Nutrient pollution can accelerate plant and algae growth.

Point source pollution – Water pollution coming from a single point or origin, such as sewage system outflow.

Reclaimed wastewater – Wastewater that has been treatedto a quality suitable for a beneficial use, such as irrigation.

Recycled water – Water that is used more than once before it returns to the natural system.

Salinity – the measure of salt dissolved in water.

Turbidity – The cloudiness of water, as caused by suspended sediments. The more turbid water is, the less available light for photosynthesis.

Wastewater treatment – The complete wastewater treatment process typically involves a three-phase process:

  1. In the primary process, untreated water is passed through a series of screens to remove solid wastes.
  2. In the secondary process, typically involving biological and chemical processes, screened wastewater is then passed through a series of holding and aeration tanks and/or ponds.
  3. The third process typically consists of filters and chlorine basins or ozone and ultraviolet radiation processes.


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