Testing
EPA primary drinking water limits, the full published chart
Quick answer
Lead has no maximum contaminant level: its action level of 0.015 mg/L triggers utility treatment steps rather than describing a safe amount, and the health goal is zero. Nitrate's 10 mg/L limit is reported as nitrogen, a different number than nitrate ion, so the units on a lab report must be read before the figure means anything.
The Environmental Protection Agency's primary drinking water standards are enforceable health limits with legal force behind them, unlike the aesthetic guidelines covered on the secondary drinking water standards chart. These are the numbers a Consumer Confidence Report is measured against, and they are also the numbers a certified laboratory report for a private well should be read against, contaminant by contaminant.
Two figures on this chart get misread more often than the rest combined, and getting either one wrong changes the advice that follows. Lead is regulated by an action level rather than a maximum contaminant level, and that distinction is not a technicality. Nitrate is reported in a unit that varies between laboratories, and using the wrong one silently moves a result by more than a factor of four.
This chart lists the primary standards. It does not diagnose your water. Bacteria, nitrate, lead, arsenic and PFAS are not do it yourself topics: confirming any of them requires a certified laboratory test, and a result at or near a limit on this page should go to your local health department or a licensed water treatment professional, not straight to a shopping cart.
The full primary standards chart
Each row below is a published EPA figure. Nothing here is rounded for convenience, and nothing here is estimated where a figure does not exist.
Lead carries an action level of 0.015 mg/L rather than a maximum contaminant level, and the health goal for lead is zero.
Published figure A published standard, regulatory limit, unit conversion or manufacturer specification. It does not change because somebody disagrees with it.
| Contaminant | Limit | Unit | Kind of limit |
|---|---|---|---|
| Lead | 0.015 | mg/L | Action level. MCLG is zero |
| Copper | 1.3 | mg/L | Action level |
| Arsenic | 0.01 | mg/L | MCL |
| Nitrate (as N) | 10 | mg/L | MCL |
| Nitrite (as N) | 1 | mg/L | MCL |
| Fluoride | 4.0 | mg/L | MCL |
| Barium | 2 | mg/L | MCL |
| Cadmium | 0.005 | mg/L | MCL |
| Chromium (total) | 0.1 | mg/L | MCL |
| Selenium | 0.05 | mg/L | MCL |
| Antimony | 0.006 | mg/L | MCL |
| Beryllium | 0.004 | mg/L | MCL |
| Mercury (inorganic) | 0.002 | mg/L | MCL |
| Thallium | 0.002 | mg/L | MCL |
| Uranium | 0.03 | mg/L | MCL |
| Radium 226 and 228 combined | 5 | pCi/L | MCL |
| Gross alpha particle activity | 15 | pCi/L | MCL |
| Total coliform and E. coli | not numeric | presence/absence | MCLG is zero; presence triggers action |
Coliform and E. coli have no numeric concentration limit because the standard is presence or absence: any confirmed presence triggers required action rather than being weighed against a threshold amount.
Why lead is an action level, not a safe amount
Lead is the contaminant on this chart most often described incorrectly. It has no maximum contaminant level at all. Instead it carries an action level of 0.015 mg/L, a regulatory trigger point that requires water utilities to take specific corrosion control and treatment steps once that many samples exceed it. The maximum contaminant level goal, the health based target with no enforcement mechanism attached, is zero. Describing 0.015 mg/L as a safe concentration to drink is a common shorthand and it is not accurate: it is the number that starts a utility's obligation to act, not a line under which lead stops mattering.
Lead mostly enters water inside a building's own plumbing, from solder, brass fittings and old service lines, rather than from the utility main, which is why a clean Consumer Confidence Report does not rule it out at your own tap. Low pH water is a related risk factor, since corrosive water mobilizes lead from those same fittings; see the pH and corrosion chart for that mechanism. Either way, lead is not a do it yourself topic: a first draw tap test read by a certified laboratory is the only way to know what is actually coming out of your own faucet, and a positive result belongs with a licensed professional or your local health department.
Why nitrate has to be read in the right units
The nitrate MCL of 10 mg/L is expressed as nitrogen, commonly written nitrate as N. Laboratories do not universally report it that way; some report nitrate as the nitrate ion itself, which is a different number for the identical water sample. A report that lists a nitrate result without saying which unit it used cannot be compared against the 10 mg/L limit safely, and the units have to be confirmed with the lab before the number means anything at all.
Nitrate is not a do it yourself topic either. It is odorless and tasteless, so a household gets no warning sign that a well has crossed the limit, and it matters most for infants, where elevated nitrate is linked to a specific and serious health risk. A result anywhere near 10 mg/L as N calls for a certified laboratory retest to confirm the unit and the number, and a conversation with your local health department rather than a filter purchase based on an assumption about which unit a lab used. A certified test like the Tap Score Advanced Home Water Test Kit, Well or City panel reports nitrate with the unit and the regulatory limit stated side by side specifically to remove that ambiguity.
PFAS: what is settled and what is not
PFAS is deliberately kept off the main chart above because part of its regulatory picture has been actively moving. Two figures are enforceable; the rest should be checked against the current EPA rule rather than any chart, including this one.
PFOA and PFOS each carry an enforceable limit of 4.0 nanograms per liter; the remaining PFAS compound limits and the mixture hazard index have since been subject to reconsideration.
Published figure A published standard, regulatory limit, unit conversion or manufacturer specification. It does not change because somebody disagrees with it.
| Compound | Limit | Unit | Status |
|---|---|---|---|
| PFOA | 4.0 | ng/L | Enforceable MCL set in the 2024 rule |
| PFOS | 4.0 | ng/L | Enforceable MCL set in the 2024 rule |
| PFHxS, PFNA, HFPO-DA, and the hazard index for mixtures | not stated here | n/a | Set in the 2024 rule and subsequently subject to reconsideration. Check the current EPA rule directly rather than any third party table |
This table intentionally omits a numeric figure for the compounds still under reconsideration. Printing a confident number that has since been withdrawn or changed would be worse than printing nothing, and the current EPA rule is the only reliable source for where those figures stand today.
Frequently asked questions
What is the EPA limit for lead in drinking water?
Lead has no maximum contaminant level. It has an action level of 0.015 mg/L, which triggers required utility treatment steps rather than describing a safe amount to drink, and the maximum contaminant level goal is zero. A result at your own tap needs a certified laboratory test, since lead mostly enters water from plumbing inside the building rather than from the utility main.
Is the nitrate limit measured as nitrate or as nitrogen?
The EPA's 10 mg/L nitrate limit is expressed as nitrogen, written nitrate as N. Some laboratories instead report the nitrate ion directly, a different number for the same water. Always confirm which unit a lab report used before comparing a result to the 10 mg/L limit, and treat any result near that limit as a reason for a certified laboratory retest.
What is the EPA limit for PFAS in drinking water?
PFOA and PFOS each carry an enforceable limit of 4.0 nanograms per liter under the 2024 national rule. Limits for several other PFAS compounds and a mixture hazard index were set in the same rule but have since been subject to reconsideration, so check the current EPA rule directly for those figures rather than any third party chart.
Does the EPA have a limit for water hardness?
No. Hardness has no maximum contaminant level and no secondary standard of any kind, because it is not classified as a health or aesthetic contaminant under EPA rules. See the secondary drinking water standards chart for what actually is regulated, and use a hardness test strip or a certified laboratory panel to measure it since no published limit exists to compare against.
What is the difference between an MCL, an MCLG and an action level?
An MCL, maximum contaminant level, is the enforceable legal limit. An MCLG, maximum contaminant level goal, is the health based target with no enforcement mechanism, often set lower than the MCL or at zero. An action level, used for lead and copper, is a concentration that triggers required utility treatment steps rather than a limit on the water itself.
Can a home test kit replace a certified laboratory test for these contaminants?
Not for the ones on this chart. Home screening kits can flag a likely problem, but bacteria, nitrate, lead, arsenic and PFAS results need confirmation by a certified laboratory before any treatment decision, since these are invisible, tasteless contaminants where an unconfirmed screen can be wrong in either direction. Treat a home kit as a first look, not a final answer.
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Researched, not professional advice. This page is compiled from published standards, regulatory limits, manufacturer specifications and owner-review consensus, not hands-on testing. Nothing here diagnoses a water problem or says any product makes water safe to drink. Figures described as a rule of thumb are water treatment trade convention rather than published standards, and they are labeled that way wherever they appear. Test your water before you buy equipment: on city water start with the Consumer Confidence Report your utility publishes each year, and on a private well only a certified laboratory test tells you what you have. Bacteria, nitrate, lead, arsenic and PFAS are not do it yourself topics, they are invisible and tasteless, and they need a laboratory and usually a licensed professional rather than a product. Remember that a certification covers a specific claim under a specific standard, so "NSF certified" with no number attached tells you very little.