University of Connecticut Cooperative Extension System: Water Quality and the Home Landscape



Water Quality Standards

Karen Filchak

The federal government sets standards for potential contaminants found in drinking water.  Two levels of standards are in place.  States also can have their own standards which will prevail only if they are more strict protective) than those set by the federal government.

The two types of standards are the National Primary Drinking Water Regulations (NPDWR), with Maximum Contaminant Levels (MCL’s) and the National Secondary Drinking Water Regulations (NSDWR).  Both apply only to public drinking water supplies though they provide the guidance for levels appropriate for private drinking water wells.

The National Primary Drinking Water Regulations are standards that are enforceable for public water systems.   Public water systems are required to regularly test for and these contaminants.  Levels must be addressed if they exceed the MCL.  The National Primary Drinking Water Standards  address contaminants that pose a health threat.


The National Secondary Drinking Water Regulations are set for contaminants that are considered a nuisance rather than a health threat.  These contaminants typically cause tease, color or odor problems which may result in common problems such as staining or clothing and plumbing fixtures.  Public water systems are not required to meet these standards but they serve as a guide for an acceptable quality of water to its consumers.  Iron and manganese are common Secondary contaminants found in CT


Meeeting primary and secondary drinking water standards assures clean drinking water at home