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.

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 Residual Disinfectant Level (MRDL): 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 contaminant.

Maximum Residual Disinfectant Level Goal (MRDLG): 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 disinfectant to control microbial contamination.

Action Level (AL)-The concentration of a contaminant which, if exceeded, may trigger additional treatment or other requirements which a water system must follow.

Treatment Technique (TT): A water Treatment Process that is established by the EPA in lieu of an MCL if the EPA finds that it is not “economically technically feasible” to determine the level of the contamination.

Unregulated Contaminants (UCMR): Unregulated Contaminants, such as NDMA, are those that don’t have a drinking water standard set by USEPA. The purpose of monitoring for these contaminants is to help EPA decide whether the contaminants should have a standard.