EPA drinking water standards table: every MCL, MCLG, action level and secondary standard a home water test reports against

If your lab report already prints an “EPA limit” column beside every result, you can leave now: these are the same numbers, and the only thing this page adds is which of them are enforceable and which are not.

Which limits are enforceable and which are not?

A Maximum Contaminant Level (MCL) is the highest concentration EPA allows in water delivered by a public water system, and it is enforceable. A Maximum Contaminant Level Goal (MCLG) is the level EPA sets as the health-based target, and it is not enforceable, which is why an MCLG can be zero while the MCL is not.

A Treatment Technique (TT) replaces an MCL where sampling every tap is impractical; lead and copper use one, with an action level triggered at the 90th percentile of sampled taps. A secondary standard is one of the 15 non-mandatory levels on EPA’s National Secondary Drinking Water Standards page, set for taste, color and odor.

Every EPA limit applies to public water systems. A private well is outside all of them; the well water test panel guide covers which results to order.

What are the EPA MCLs for inorganic chemicals?

All values are copied from EPA’s National Primary Drinking Water Regulations page and shown in mg/L, the same as parts per million (ppm).

Nitrate and nitrite are stated as nitrogen. A lab reporting “nitrate as NO3” uses a different scale, so read the unit line before comparing against 10 mg/L; the nitrate guide shows the conversion.

What are the EPA limits for radionuclides?

EPA’s NPDWR page prints these in the units a lab uses; the table keeps them and adds mg/L where one exists.

Radon has no federal MCL in force on EPA’s NPDWR page; the uranium and radon in well water guide covers what a lab result for either means.

What is the PFAS rule as of 2026?

EPA’s 2024 PFAS National Primary Drinking Water Regulation is the first federal MCL for these compounds. The table gives the limits as EPA prints them, in parts per trillion (ppt, the same as ng/L), plus the mg/L equivalent.

EPA’s PFAS page gives public water systems three years to complete initial monitoring, by 2027, and the compliance-extension page states MCL compliance is due April 2029 under the rule as written.

EPA’s Proposed PFOA and PFOS Compliance Extension Rule would grant systems two additional years, to April 2031; its comment period closed July 20, 2026, after a virtual hearing on July 7, 2026, under docket EPA-HQ-OW-2025-1742. EPA’s Proposed PFAS Rescission Rule would withdraw the determinations for PFHxS, PFNA, HFPO-DA and the Hazard Index mixture of those three plus PFBS, and its page was last updated July 23, 2026 with the rule still proposed.

The 4.0 ppt figures for PFOA and PFOS are not part of either proposal. What a home filter can do about a PFAS result is on the PFAS in tap water guide.

What is the lead action level?

EPA’s NPDWR page states it directly: beginning on the LCRI compliance date of November 1, 2027, systems must comply with the revised lead action level of 0.010 mg/L. An action level is a system-wide trigger, not a limit on your tap, so one kitchen sample above 0.015 mg/L does not by itself put a utility out of compliance. The lead guide covers the service-line check.

What are the EPA secondary standards?

EPA’s National Secondary Drinking Water Standards are non-mandatory. EPA describes them as guides for aesthetic considerations such as taste, color and odor, and does not enforce them.

Copper and fluoride appear in both tables with different numbers: the primary copper action level is 1.3 mg/L and the secondary level is 1.0 mg/L; the primary fluoride MCL is 4.0 mg/L and the secondary standard is 2.0 mg/L. The lower figure in each pair is the taste and staining guide, the higher one the enforceable limit. Hardness is on neither list; the hard water guide covers the gpg scale, and a TDS meter reading guide in this series explains why a 500 mg/L TDS reading says nothing about which contaminant is present.

What should you do first?

1. Read the unit line on your report and convert to mg/L before comparing: 1 ppm equals 1 mg/L, 1 ppb equals 0.001 mg/L, 1 µg/L equals 0.001 mg/L.
2. Mark every result above its MCL or action level in the primary tables; those are the enforceable ones.
3. Mark every result above a secondary standard separately; those explain taste, stain and odor, not compliance.
4. For lead, note whether the sample was first-draw or flushed; the action level is a 90th-percentile system figure and a single tap result is read differently.
5. Open the linked guide for each marked line to see the treatment class; where none is linked, ask your state drinking water program which local limit applies.

Frequently asked questions

Sources

1. EPA, National Primary Drinking Water Regulations (government or regulatory source)
2. EPA, Per- and Polyfluoroalkyl Substances (PFAS) National Primary Drinking Water Regulation (government or regulatory source)
3. EPA, Proposed PFOA and PFOS Compliance Extension Rule (government or regulatory source)
4. EPA, Proposed PFAS Rescission Rule (government or regulatory source)
5. EPA, Secondary Drinking Water Standards: Guidance for Nuisance Chemicals (government or regulatory source)