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Drinking Water Regulations and Contaminants

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National Primary Drinking Water Regulations (NPDWRs)

NPDWRs (or primary standards) are legally enforceable standards that apply to public water systems.

Primary standards protect public health by limiting the levels of contaminants in drinking water.

List of Primary Drinking Water Contaminants and their Maximum Contaminant Levels (MCLs)


National Secondary Drinking Water Regulations (NSDWRs)

NSDWRs (or secondary standards) are non-enforceable guidelines regulating contaminants that may cause cosmetic effects (such as skin or tooth discoloration) or aesthetic effects (such as taste, odor, or color) in drinking water. EPA recommends secondary standards to water systems but does not require systems to comply with the standard. However, states may choose to adopt them as enforceable standards.

While secondary standards are not federally enforceable, EPA requires a special notice for exceedance of the fluoride secondary standard of 2.0 mg/L. Community water systems that exceed the fluoride secondary standard of 2 mg/L, but do not exceed the primary standard of 4.0 mg/L for fluoride, must provide public notice to persons served no later than 12 months from the day the water system learns of the exceedance (40 CFR 141.208).

List of National Secondary Drinking Water Regulations
Contaminant Secondary Standard
Aluminum 0.05 to 0.2 mg/L
Chloride 250 mg/L
Color 15 (color units)
Copper 1.0 mg/L
Corrosivity noncorrosive
Fluoride 2.0 mg/L
Foaming Agents 0.5 mg/L
Iron 0.3 mg/L
Manganese 0.05 mg/L
Odor 3 threshold odor number
pH 6.5-8.5
Silver 0.10 mg/L
Sulfate 250 mg/L
Total Dissolved Solids 500 mg/L
Zinc 5 mg/L

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Unregulated Drinking Water Contaminants

This list of contaminants which, at the time of publication, are not subject to any proposed or promulgated national primary drinking water regulation (NPDWRs), are known or anticipated to occur in public water systems, and may require regulations under the Safe Drinking Water Act (SDWA).

For more information visit the Drinking Water Contaminant Candidate List (CCL) and Regulatory Determination Website.