Glossary

• 1 mg/L
  1 mg/L or milligram per liter represents 1 part per million (ppm). An example of a part per million is one cent in $10,000.
• 1 ug/L
  1 ug/L or microgram per liter represents 1 part per billion (ppb). An example of a part per billion is one cent in $10 million.
• Action Level (AL)
  The concentration of a contaminant which, if exceeded, triggers treatment or other actions which a water system must take.
• Activated Carbon
  Activated carbon filters absorb impurities from water such as odors, tastes, organic compounds and residual chlorine. Carbon filters also remove radon gas and hydrogen sulfide. Most inorganic chemicals are not removed by these filters.
• Acute Health Effect
  An immediate (i.e., within hours or days) adverse health effect that may result from exposure to certain drinking water contaminants (e.g., pathogens).
• Aesthetic
  Contaminant which may affect water quality such as taste, color or odor.
• Anion Exchange
  Anion exchange units contain a resin that exchanges chloride or hydroxide ions for contaminant anions such as fluoride, nitrate, sulfate and bicarbonates to purify the water.
• ANSI
  American National Standards Institute. ANSI administers and coordinates the U.S. voluntary standardization and conformity assessment system. UL is accredited through ANSI to perform testing on drinking water treatment units in accordance with industry standards.
• cfu
  Colony Forming Unit. A bacterial colony presumed to have originated from a single bacterium present in the sample.
• Chronic Health Effect
  The possible result of exposure over many years to a drinking water contaminant at a concentration above its Maximum Contaminant Level.
• Disinfectant
  A chemical (commonly chlorine, chloramines, or ozone) or physical process (e.g., ultraviolet light) that kills microorganisms such as bacteria, viruses and protozoa.
• Disinfectant Byproduct
  Chemicals that may form when disinfectants (such as chlorine), react with plant matter and other naturally occurring materials in water. Exposure to these chemicals may pose health risks.
• Distillation
  Distillation is a process of heating water until it evaporates as steam leaving behind bacteria, minerals, trace amounts of metals, sodium chloride, organic chemicals and nitrate.
• Federal Limit
  Maximum allowable concentration of a contaminant in a public water supply. This applies to primary and secondary limits.
• Ground Water
  Ground water is the water found underground in the spaces between particles of rock and soil.
• Herbicide
  A chemical compound, usually synthetic, used to control weeds.
• Industrial Chemical
  Chemicals used or produced primarily in industrial applications.
• Inorganic Contaminants (IOC)
  Mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally occurring in some water, but can also enter water through farming, chemical manufacturing and other human activities.
• Ion Exchange
  Ion (anion or cation) exchange systems soften hard water by removing the minerals (calcium and magnesium) that cause hardness. Ion exchange units also remove iron, manganese and many heavy metals. The hard water is pumped through a tank containing an exchange resin. Sodium on the resin replaces the hardness minerals. The sodium remains in a soluble form in the softened water.
• Maximum Contaminant Level (MCL)
  The highest concentration of a contaminant that is allowed in drinking water. MCLs are set as close to the MCLG as feasible using the best available treatment technology and taking cost into consideration.
• Maximum Contaminant Level Goal (MCLG)
  The concentration of a contaminant in drinking water below which there is no known or expected risk to health. MCLGs are non-enforceable health goals.
• Mechanical Filter
  Mechanical filters remove suspended material from water including sand, silt, clay or organic matter. These filters do not remove dissolved or very fine particles and are often used in combination with other treatment equipment.
• National Primary Drinking Water Standards
  Legally enforceable standards that apply to public water systems. These standards limit the concentrations of specific contaminants that can adversely affect public health and which are known or anticipated to occur in public water supplies.
• NTU
  NTU stands for Nephelometric Turbidity Unit which is the unit used to measure turbidity in water. Turbidity refers to the scattering and absorption of light rather than transmission caused by suspended matter such as clay, dissolved organic material and microscopic organisms.
• Organic Contaminants
  Carbon-based chemicals, such as solvents and pesticides, which can enter drinking water supplies through runoff from cropland, discharges from industrial operations, underground tanks, spills and other sources.
• Pesticide
  A synthetic chemical, used to control pests such as insects and other invertebrates such as worms and nematodes.
• Radionuclide
  An unstable form of a chemical element that radioactively decays, resulting in the emission of nuclear radiation.
• Reporting Limit
  The lowest concentration at which a contaminant is reported.
• Reverse Osmosis
  Reverse Osmosis units remove most inorganic chemicals such as salts, metals and minerals as well as microorganisms and many (but not all) organic compounds. Reverse Osmosis units are often used in conjunction with mechanical and activated carbon filters. Reverse Osmosis units use large amounts of water, usually 75% is discarded with the contaminants.
• Secondary Drinking Water Standards
  Non-enforceable federal guidelines regarding cosmetic effects (such as tooth or skin discoloration) or aesthetic effects (such as taste, odor or color) of drinking water.
• Secondary Maximum Contaminant Level (SMCL)
  Non-enforceable federal limits set for contaminants included in the Secondary Drinking Water Standards. The purpose of these limits is to assist public water systems in managing their drinking water for aesthetic considerations.
• Treatment Technique (TT)
  A process required by public water systems to reduce the concentration of a contaminant in drinking water.
• Ultraviolet Disinfection
  Ultraviolet (UV) light is used to kill or deactivate pathogens such as bacteria and viruses. Unlike chemical disinfectants such as chlorine, UV does not leave a residual product.
• Volatile Organic Contaminant (VOC)
  Group of organic chemicals characterized by their volatility (ability to evaporate). Volatile organic chemicals are components of gasoline and are widely used in the manufacture of plastics, clothing and other common household items.