Useful Drinking Water Terms and Definitions

• AL (Action Level): The concentration of a substance which, if exceeded, triggers treatment or other requirements that a water system must follow.
• BDL (Below Detection Level): The substance could not be found at the minimum amount that can be reliably detected.
• GPG (Grains Per Gallon): Unit of water hardness.
• MCL (Maximum Contaminant Level):The highest amount of a substance allowed in drinking water. MCLs are set as close to the MCLGs as feasible using the best available treatment technology.
• MCLG (Maximum Contaminant Level Goal):The level of a substance below which there is no known or expected risk to health. MCLGs allow for a margin of safety.
• MRDL (Maximum Residual Disinfectant Level): The highest level of a disinfectant allowed in drinking water. There is convincing evidence that addition of a disinfectant is necessary for control of microbial contaminants.
• MRDLG (Maximum Residual Disinfectant Level Goal): The level of a drinking water disinfectant below which there is no known or expected risk to health. MRDLGs do not reflect the benefits of the use of disinfectants to control microbial contamination.
• NA (Not Applicable): Data not available.
• NTU (Nephelometric Turbidity Units): Cloudiness of the water.
• pCi/L (Picocuries per Liter): A measure of radioactivity.
• PPM (Parts Per Million): Also referred to as milligrams per liter.
• PPB (Parts Per Billion): Also referred to as micrograms per liter.
• PPT (Parts Per Trillion): Also referred to as nanograms per liter.
• TT (Treatment Technique): A required process intended to reduce the level of a contaminant in drinking water.