Maximum Contaminant Level Goal (MCLG): The level of a contaminant in drinking water below which there is no known or expected risk to health.  MCLGs allow for a margin of safety.

Maximum Contaminant Level (MCL): The highest level of contaminant that is allowed in drinking water.  MCLs are set as close to the MCLGs as feasible using the best available treatment technology.

Parts per Million (ppm)  or Milligrams per Liter (mg/L) are units of measure for concentration of a contaminant.  A part per million corresponds to one second in approximately 11.5 days. 

Parts per Billion (ppb) or Micrograms per Liter (μg/L) are units of measure for concentration of a contaminant.  A part per billion corresponds to one second in 31.7 years.

Action Level (AL): The concentration of a contaminant which, if exceeded, triggers treatment or other requirements which a water system must follow.

Action Level Goal (ALG): The level of contaminant in drinking water below which there is no known or expected risk to health. ALGs allow for a margin of safety.

Maximum Residual Disinfectant Level Goal (MRDLG): The level of drinking water disinfectant below which there is no known or expected risk to health.  

Maximum Residual Disinfectant Level (MRDL): The highest level of a disinfectant allowed in drinking water.  

Million Fibers per Liter (MFL) millirems per year (mrem/year)pico Curies per liter is a measure of radioactivity = pCi/L.

The “<“ symbol: A symbol which means less than.  A result of <5 means that the lowest level that could be detected was 5 and the contaminant in that sample was not detected.