Three groups, and the group decides what you can do
Every contaminant page on this site belongs to one of three categories. The
distinction is not how dangerous something sounds. It is whether a number binds
anyone.
Enforceable. A maximum contaminant level or treatment technique your utility
must meet, reported annually. Lead, nitrate, asbestos, the disinfection
byproducts, the radionuclides.
Advisory. A figure exists and obliges nobody. EPA enforces none of the 15
secondary standards, and describes health advisories as “informal technical
guidance.”
Manganese, cyanotoxins and the taste and colour standards live here.
Unmeasured. No limit, and often no monitoring. The Contaminant Candidate
List and the five-yearly Unregulated Contaminant Monitoring Rule are the two
mechanisms watching this space.
What to check, in what order
Start with whether a number binds anyone
Read the enforceable line first, because it is the only one with a duty
attached. A maximum contaminant level obliges your utility to act and to tell
you when it fails; a secondary standard or health advisory does neither.
EPA states plainly that it does not enforce secondary maximum contaminant levels
and that systems test for them only on a voluntary basis, so a blank line may
mean nobody measured rather than nothing was found. That distinction resolves
most of what households get wrong here.
Then check whether the limit is the health goal
A compliant result is not always a reassuring one. For most contaminants the
maximum contaminant level goal sits below the enforceable limit, and the band
between them is lawful, unflagged and invisible on a report. Lead’s goal is
zero against an action level of 10 micrograms per litre. Nitrate and asbestos
are the exceptions where goal and limit coincide, which means a compliant figure
there is measured against the health figure itself rather than a compromise.
Then ask whether anything is certified for it
Certification is a separate system from regulation and neither contains the
other. Crossing EPA’s 94 regulated entries against NSF’s claim list leaves 33
with no certified reduction claim of that name, including vinyl chloride,
glyphosate and uranium. Meanwhile microcystin and radon carry certified claims
with no enforceable limit behind them at all. Knowing which side of that
mismatch your contaminant sits on tells you whether a purchase can be verified.
Where each contaminant sits
| Contaminant |
Status |
Certified claim exists |
| Lead |
Action level, 10 µg/L |
Yes, 615 models |
| Nitrate |
Limit, goal equals limit |
Yes, 84 models |
| PFAS |
Limits for six, four proposed for rescission |
PFOA and PFOS only |
| Copper |
Action level and secondary standard |
Yes |
| Fluoride |
Limit, plus a secondary with a notice duty |
Yes, 127 models |
| Disinfection byproducts |
Limits for TTHM and HAA5 |
TTHM yes, HAA5 no |
| Chromium-6 |
Total chromium limit only |
Yes, 120 models |
| Asbestos |
Limit, goal equals limit |
Yes, 264 models |
| Radium and uranium |
Limits for four radionuclides |
Radium only |
| Radon |
No limit — 1999 rule never finalised |
Yes, 30 models |
| Cyanotoxins |
Advisory only |
Microcystin only |
| Manganese |
Advisory and secondary |
No |
| Microplastics |
No limit |
Yes, 806 models |
| Pharmaceuticals |
No limit, no monitoring |
Yes, seven claims |
| Legionella |
Treatment technique, no limit |
No |
| TDS |
Secondary, unenforced |
Yes, under NSF/ANSI 58 |
Choose what to act on
Act on it if it carries an enforceable limit and your report shows a figure
at or near that limit. That is the only combination giving you both a duty and a
number.
Investigate it if the figure is advisory, or the line is blank on a report
where monitoring was voluntary. Neither is a result.
Leave it if nothing measures it and nothing certifies against it. There is
no threshold to treat to and no product to verify.
The two pages that hold the cross-cuts
Two pages exist because the mismatch between regulation and certification is
itself the finding.
The regulated contaminants with no certified filter
takes the 33 entries EPA regulates and NSF does not name.
Unregulated contaminants takes the opposite case —
the candidate list, the monitoring rule, and the reporting floor that is set by
what laboratories can achieve rather than by health.
Start with the report, not the worry
Nothing in this cluster is worth acting on before you have read the document
your utility already sends you. It names your source, your treatment and every
regulated contaminant detected.
→ How to read your water quality report
→ City water treatment, and the three gaps a utility cannot close
→ Which claims exist at all, and how populated each is
→ Testing city water: what your utility already measured
→ Why your water tastes, smells or looks wrong
The bottom line
Sort by what binds before you sort by what worries you. A contaminant with an enforceable limit gives you a figure on your report and, often, a certified filter to match it. An advisory figure gives you neither obligation nor remedy. An unmeasured one gives you nothing to act on at all. Most household spending goes wrong at this first step, treating the three as though they were the same kind of thing.
Who this is not for
This is a map, not a diagnosis. It cannot tell you what is in your water — that comes from your utility's annual report, and for anything picked up in your own plumbing, from a test of your own tap. It covers public water systems; private wells sit outside every limit discussed here.
Questions
How do I tell which contaminants actually matter?
Start with whether a number binds anyone. An enforceable maximum contaminant level obliges your utility to act and appears on your annual report. A secondary standard or health advisory obliges nobody, and EPA says so directly in both cases.
Does a limit mean the water is safe below it?
Not in the way most people read it. For several contaminants the health goal sits below the enforceable limit, and the gap between them is legal and unflagged. For nitrate and asbestos the two figures coincide, which is unusual.
Are unregulated contaminants unmonitored?
Not always. The Contaminant Candidate List names contaminants that may warrant future regulation, and the Unregulated Contaminant Monitoring Rule requires a fresh round of national sampling every five years. Results reach the annual report when detected.
If something is regulated, is there a filter for it?
Often, but not reliably. Crossing EPA's regulated entries against NSF's claim list leaves 33 regulated contaminants with no certified reduction claim of that name. Certification follows what manufacturers test, not what EPA regulates.
Can an unregulated contaminant have a certified filter?
Yes, and several do. Microcystin has no enforceable limit and 48 certified models. Radon in water has no limit and 30. The certified market and the regulated list overlap without either containing the other.
Which contaminants come from my own plumbing?
Lead and copper chiefly, which are picked up downstream of every sample your utility takes. That is why they are handled through an action level and household sampling rather than through treatment at the plant alone.
Where do I start if I have read nothing?
Your annual report. It names the source, the treatment and every regulated contaminant detected, and it arrives by 1 July each year. Nothing on this cluster is worth acting on before you have read it.
Sources — 12 claims
- EPA — Secondary Drinking Water Standards: Guidance for Nuisance Chemicals
EPA does not enforce Secondary Maximum Contaminant Levels; they are guidelines established for aesthetic considerations. (captured 2026-09-09) - EPA — Secondary Drinking Water Standards: Guidance for Nuisance Chemicals
EPA has established National Secondary Drinking Water Standards setting non-mandatory levels for 15 contaminants, states it does not enforce them, and states that because they are not health threatening at the secondary maximum contaminant level, public water systems only need to test for them on a voluntary basis. (captured 2026-09-11)
Limits: Federal position only. States may adopt secondary standards as enforceable requirements of their own, and many public water systems monitor them voluntarily. A figure absent from a Consumer Confidence Report may simply never have been measured. - EPA — Drinking Water Health Advisories for Cyanotoxins
EPA states that under the Safe Drinking Water Act it may publish Health Advisories for contaminants not subject to any national primary drinking water regulation, that these describe concentrations at which adverse health effects are not anticipated over specific exposure durations such as one day, ten days, several years and a lifetime, that they contain a margin of safety, and that they serve as informal technical guidance to assist officials and water system managers. (captured 2026-09-11)
Limits: A health advisory binds nobody. No utility is judged against one, no violation follows from exceeding one, and no notification duty attaches. It is the same class of figure as the manganese health advisory already recorded on this site. - EPA — Contaminant Candidate List 5 (CCL 5), page last updated 2026-02-27
EPA defines the Contaminant Candidate List as contaminants that are not subject to any proposed or promulgated national primary drinking water regulation but are known or anticipated to occur in public water systems, and which may require future regulation. CCL 5, published 14 November 2022, contains 66 chemicals, three chemical groups — PFAS, cyanotoxins and disinfection byproducts — and 12 microbes. (captured 2026-09-11)
Limits: A candidate list, not a regulation and not a warning. Listing means EPA considers a contaminant a priority for regulatory decision-making and information collection. It sets no limit, obliges no utility to do anything, and implies nothing about concentration in any particular supply. - EPA — Fifth Unregulated Contaminant Monitoring Rule (UCMR 5)
The Safe Drinking Water Act requires EPA to issue a list of unregulated contaminants for public water systems to monitor once every five years. UCMR 5, published 27 December 2021, required sampling for 30 chemical contaminants — 29 PFAS and lithium — between 2023 and 2025, and EPA released the final dataset in August 2026. (captured 2026-09-11)
Limits: Monitoring, not regulation. A UCMR result carries no limit to comply with and no violation to declare. The 29 PFAS were included because the National Defense Authorization Act for Fiscal Year 2020 required EPA to include all PFAS with a validated drinking water method that were not already regulated. - Crosswalk of EPA National Primary Drinking Water Regulations against the NSF reduction-claim taxonomy (both captured 2026-09-10)
Crossing EPA 94 regulated contaminant entries against NSF 101 selectable reduction claims on 2026-09-10 leaves 33 regulated contaminants with no NSF reduction claim of that name: 19 organic chemicals, 4 microorganisms, 4 inorganic chemicals, 3 disinfection byproducts and 3 radionuclides. (captured 2026-09-10)
Limits: The absence of a claim by name is not evidence that no product treats the contaminant. Reverse osmosis and distillation remove many of these; NSF offers no named claim to certify them against. NSF offers no claims at all under its distillation standard, so distillation is invisible to this crosswalk, and microorganisms are certified through NSF/ANSI 55 disinfection performance classes rather than by contaminant. - EPA — Basic Information about Lead in Drinking Water
EPA has set the Maximum Contaminant Level Goal for lead in drinking water at zero, because the best available science shows there is no safe level of exposure to lead. (captured 2026-09-10)
Limits: The MCLG is a non-enforceable health goal, not a limit a utility must meet. The enforceable trigger is the action level, which is a separate and higher number. - EPA — National Primary Drinking Water Regulations, inorganic chemicals table
EPA sets the nitrate maximum contaminant level at 10 mg/L measured as nitrogen and the maximum contaminant level goal at the same figure, 10 mg/L. Nitrite is 1 mg/L for both. For most regulated contaminants the health goal sits below the enforceable limit or at zero; for nitrate and nitrite the two are identical. (captured 2026-09-11)
Limits: An MCLG equal to the MCL means EPA judged the enforceable limit achievable at the health goal rather than as a compromise. It is not a statement that any level below 10 mg/L is without effect, and Minnesota Department of Health separately describes emerging science on long-term exposure below the standard. - EPA — National Primary Drinking Water Regulations, inorganic chemicals table
EPA regulates asbestos in drinking water at 7 million fibres per litre, counting only fibres longer than 10 micrometers, and sets the maximum contaminant level goal at the same figure. It names the health effect of long-term exposure above the limit as increased risk of developing benign intestinal polyps, and the sources as decay of asbestos cement in water mains and erosion of natural deposits. (captured 2026-09-11)
Limits: The standard counts only fibres longer than 10 micrometers, so shorter fibres are outside what the limit measures. The goal equalling the limit means EPA judged the enforceable figure achievable at the health goal. This is the ingestion route only; EPA describes a different route and different effects for airborne asbestos. - EPA — National Primary Drinking Water Regulations, microorganisms table and Surface Water Treatment Rule footnotes
EPA lists Legionella in its regulated microorganisms with a maximum contaminant level goal of zero and a treatment technique rather than a numeric limit. It names the health effect as Legionnaire's Disease, a type of pneumonia, and the source as found naturally in water, multiplying in heating systems. (captured 2026-09-11)
Limits: A treatment technique applies to the water system, not to a household. The phrase "multiplies in heating systems" points at where the organism grows, which is downstream of anything a utility controls. - EPA — National Primary Drinking Water Regulations, full regulated contaminant table
Radon appears nowhere in EPA's National Primary Drinking Water Regulations table of regulated contaminants on 2026-09-11, so there is no maximum contaminant level, no treatment technique and no enforceable standard for radon in drinking water. The 1999 proposed rule was never finalised. (captured 2026-09-11)
Limits: Established by searching EPA's current regulated contaminant table for radon and finding no entry, with radium and uranium each returning exactly one entry as positive controls, so the search works and the absence is real. EPA separately states the gross alpha standard covers all alphas but does not include radon. - EPA — Drinking Water Health Advisories for Cyanotoxins
EPA published ten-day drinking water health advisories for two cyanotoxins in 2015. For microcystins the values are 0.3 µg/L for bottle-fed infants and pre-school children and 1.6 µg/L for school-age children and adults. For cylindrospermopsin they are 0.7 µg/L and 3.0 µg/L for the same two groups. (captured 2026-09-11)
Limits: Ten-day values, not lifetime limits, and not enforceable. They are set for a short exposure such as a bloom event. EPA also produced a health effects support document for anatoxin-a but published no health advisory value for it.