EPA Definitions

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 are non-enforceable public-health goals.

Maximum Contaminant Level (MCL): The highest level of a contaminant that is allowed in drinking water. MCLs are set as close to MCLGs as feasible using the best available treatment technology and taking cost into consideration. MCLs are enforceable standards for public water-supply systems.

Secondary Maximum Contaminant Level (SMCL): Non-enforceable guidelines regarding chemicals that may cause cosmetic or aesthetic effects in drinking water. EPA recommends these secondary standards but does not require water-supply systems to comply.