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Understanding EPA Primary and Secondary Drinking Water Standards

The United States Environmental Protection Agency develops drinking water standards based on the Safe Drinking Water Act (SWDA). The SWDA authorizes EPA to set nation-wide standards in order to protect the nation’s drinking water. These regulations apply only to municipal drinking water systems. Although wells are not covered under SWDA regulations, the same water quality standards should be applied by private well owners to ensure safe drinking water. EPA periodically reviews individual contaminants and water treatment chemicals to maintain The National Primary Drinking Water Regulations (NPDWR). These regulations are legally enforceable for primary contaminant levels and water treatment practices. The primary contaminants are selected because they are a potential health concern and there is a strong chance that the contaminants will be found in the water supply at levels that will affect public health. EPA sets enforceable Maximum Contaminant Levels or MCLs for the primary standards. EPA delegates the responsibilities for maintaining these levels to the individual Sates. States can choose to adopt the EPA Maximum Contaminant Levels or create more stringent levels for their state. The general categories of the primary drinking water standards include:
  • Microorganisms
  • Disinfectants
  • Disinfectant Byproducts
  • Inorganic chemicals
  • Radionuclides
Understanding EPA Primary and Secondary Drinking Water Standards

EPA Primary Drinking Water Contaminants

Inorganic Chemicals

Organic Chemicals


  • Radon
  • Uranium

The EPA also sets National Secondary Drinking Water Regulations (NSDWR). Secondary drinking water standards are not Federally enforceable but serve as a guideline for the States to follow. Fluoride is the exception, requiring public notification if treatment levels exceed the standard. Secondary contaminants relate to substances that are not health hazards or are present at levels that are known to be harmful. These substances can cause cosmetic effects such as skin, hair and tooth discolorations. Aesthetic effects include objectionable tastes, colors and odors in the water. Individual states may choose to have stricter regulations for secondary contaminates and develop their own enforceable standards. At present, there are 15 NSDWR contaminants.

  • Aluminum
  • Chloride
  • Color
  • Copper
  • Corrosivity
  • Fluoride
  • Foaming agents
  • Iron
  • Manganese
  • Odor
  • pH
  • Silver
  • Sulfate
  • Total dissolved solids
  • Zinc

These secondary contaminants, while not usually a health hazard, can cause “technical” problems such as damage to water filtration equipment, faucets, showers, washing machines, water heaters and many more home and industrial operations. For example, colors caused by natural tannins, copper or iron can cause problems with food preparation, hair dyes and stain clothing, sinks and toilets.

It is worth noting that many residential, institutional and industrial water consumers want or need water with a higher purity than the EPA standards. What may pass as acceptable by Federal regulations is unacceptable for use in the home, factory, laboratory, commercial laboratory, greenhouse or healthcare facility. At WECO we understand water filtration and how it relates to every application ranging from home water softening to high-volume reverse osmosis systems for commercial use. Our engineers can design a water filtration system for any application, large or small. WECO is a US-based company founded on providing the right solutions to your individualized needs. Our Certified Water Specialists are here to answer your questions and provide product support whenever you need it.

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