Testing
How to read a water quality report, line by line
Quick answer
A water quality report mixes three different kinds of limit that look identical in a table: an enforceable MCL, a health goal called the MCLG, and an action level like lead at 0.015 mg/L, which triggers utility steps rather than marking a safe concentration. Reading which one applies changes what a number actually means.
A Consumer Confidence Report or a private laboratory report looks like a simple table: a contaminant name, a number, and a limit. In practice it packs three fundamentally different kinds of limit into that same column, plus units that change what a number means depending on how it is reported, and getting any of that wrong is how a perfectly normal result gets read as a crisis, or a genuine problem gets waved off as nothing.
This guide is the decoder. It does not replace getting a test in the first place, and it does not diagnose your specific report. What it does is explain what each column actually means so the number in front of you says what you think it says.
On this page
- What a Consumer Confidence Report actually tells you
- Three kinds of limit, and they are not interchangeable
- Read the units before you read the number
- Primary standards are enforceable health limits. Secondary standards are not.
- PFAS: the section of the report most likely to be out of date
- Reading a report line by line
- A private well report uses the same numbers as a benchmark, not as a legal limit
What a Consumer Confidence Report actually tells you
Every community water system publishes this report once a year, free, and it lists the regulated contaminants the utility tested for, the result, and the limit it is measured against. It reflects water at the treatment plant and in the distribution system, which is the part the utility controls directly.
What it does not reflect is anything that changes once water leaves the main and enters your own plumbing, and lead is the clearest example. Lead has no maximum contaminant level at all, only an action level of 0.015 mg/L that triggers utility treatment steps rather than describing a safe concentration, and the health goal, the MCLG, is zero. Lead typically comes from solder, fittings and service lines inside a house rather than from the treatment plant, so a clean annual report says nothing about lead at your own faucet. That needs its own first draw test at the tap, and any detectable result deserves a certified laboratory confirmation and a conversation with a licensed professional, since lead is not a do it yourself problem.
Three kinds of limit, and they are not interchangeable
Lead has no enforceable MCL at all, only an action level of 0.015 mg/L that triggers utility treatment steps, while the health goal for lead sits at zero.
Published figure A published standard, regulatory limit, unit conversion or manufacturer specification. It does not change because somebody disagrees with it.
| Term | What it means |
|---|---|
| MCL, maximum contaminant level | The enforceable legal limit for that contaminant in treated drinking water |
| MCLG, maximum contaminant level goal | The health based goal with no legal force. For lead and for total coliform, the goal is zero |
| Action level | A trigger for utility treatment steps rather than a safe concentration. Lead is the main example, at 0.015 mg/L |
A number sitting below an action level is not the same statement as a number sitting below an MCL. The action level exists because lead has no achievable enforceable limit in the way most contaminants do, and describing 0.015 mg/L as a safe amount of lead is a common and meaningful misreading of the report.
Read the units before you read the number
Milligrams per liter and parts per million are the same unit for water this dilute, so those two do not trip anybody up. The unit that does is nitrate, because it can be reported as nitrate as nitrogen or as the nitrate ion itself, and those are two different numbers describing the same water. The federal limit of 10 mg/L applies to nitrate as N. A laboratory reporting nitrate as the ion instead produces a larger number for identical water, so the units printed on the report line have to be read before the figure means anything, and nitrate deserves that care because it is especially serious for infants.
PFAS results are typically reported in nanograms per liter rather than milligrams per liter, a thousand times smaller a unit, because the enforceable limits are that small: the 2024 rule set PFOA and PFOS at 4.0 ng/L each. Radiological results, like combined radium 226 and 228, use picocuries per liter, a unit specific to radioactivity rather than mass concentration. None of these convert to each other, and mixing them up by a factor of a thousand is an easy way to misread a report as either far worse or far better than it actually is.
PFAS limits are set in nanograms per liter, a thousand times smaller a unit than the milligrams per liter used for most other contaminants.
Published figure A published standard, regulatory limit, unit conversion or manufacturer specification. It does not change because somebody disagrees with it.
| Contaminant | Unit used | Watch for |
|---|---|---|
| Most metals and general chemistry | mg/L (equivalent to ppm) | Straightforward, no conversion needed |
| Nitrate | mg/L, but check whether it is "as N" or as the ion | The MCL of 10 mg/L applies to nitrate as N specifically |
| PFOA and PFOS | ng/L | A thousand times smaller than mg/L; do not compare directly to metals |
| Radium 226 and 228 combined | pCi/L | A radioactivity unit, not a mass concentration |
Primary standards are enforceable health limits. Secondary standards are not.
The report usually lists both kinds of standard in the same table, which is exactly why hardness and iron get treated as a health emergency far more often than they deserve to be. Primary standards, like the arsenic MCL of 0.010 mg/L or the nitrate MCL of 10 mg/L, are enforceable and health based. Secondary standards, like iron at 0.3 mg/L, manganese at 0.05 mg/L, total dissolved solids at 500 mg/L or pH between 6.5 and 8.5, are aesthetic guidelines: they describe staining, taste and appearance, not an enforceable health limit.
Hardness does not appear on either list at all. There is no EPA maximum contaminant level and no secondary standard for hardness of any kind, because it is not a health contaminant. A great deal of softener marketing implies otherwise, and a report will never contradict that marketing directly since hardness simply is not a regulated line item to begin with.
PFAS: the section of the report most likely to be out of date
The 2024 national primary drinking water regulation set enforceable limits of 4.0 ng/L each for PFOA and PFOS. Limits for several additional PFAS compounds and a hazard index for mixtures were part of the same rule and have since been subject to reconsideration, with compliance timelines moving as a result. State the PFOA and PFOS figure with confidence, since that piece is settled, and treat anything beyond it as a moving target: check the current EPA rule directly for the rest rather than trusting any third party table, including this one, to have the latest version.
Reading a report line by line
- Find the contaminant name and its units. Confirm whether you are looking at mg/L, ng/L or pCi/L before comparing anything, since the wrong unit assumption changes the answer by orders of magnitude.
- Identify which kind of limit applies. Check whether the column is labeled MCL, MCLG or action level. Lead specifically carries no MCL, only an action level, and treating 0.015 mg/L as a safe number rather than a trigger is the most common misreading on the whole report.
- Check whether it is a primary or secondary standard. A secondary standard violation, like iron or manganese above the aesthetic guideline, is a staining and taste issue rather than a health limit. A primary standard violation is enforceable and health based, and deserves to be taken seriously as such.
- Confirm the report year is current. A Consumer Confidence Report covers a specific calendar year. Confirm you are reading the most recent one your utility has published rather than an older copy that happens to be the one you found first.
- Remember what the report does not cover. Lead at your own tap is not on this report. If your home has any possibility of lead solder, fittings or a lead service line, a separate first draw test is the only way to know, regardless of how clean the rest of the report looks.
A private well report uses the same numbers as a benchmark, not as a legal limit
A laboratory report on well water is not measured against any legal requirement, because nobody regulates a private well the way a community system is regulated. The same published EPA figures still function as the useful benchmark, since they represent the health based research behind each limit rather than an accident of which water source happens to be regulated. A well reading above the nitrate MCL of 10 mg/L as N is exactly as serious as a community system reading the same number, even though only one of them faces a legal consequence for it.
Frequently asked questions
What is the real difference between MCL and MCLG?
The MCL is the enforceable legal limit a water system must meet. The MCLG is the health based goal with no legal force behind it, set at the level with zero expected health risk. For lead and for total coliform bacteria, the MCLG is zero, which is why a number just under the lead action level should never be read as officially safe rather than as below a regulatory trigger.
Why does my report not list a normal limit for lead?
Because lead has no maximum contaminant level at all. It has an action level of 0.015 mg/L, which triggers required utility treatment steps rather than describing a safe concentration, and the health goal is zero. Lead also mostly comes from plumbing inside a building rather than the treatment plant, so the annual report cannot capture it at your own tap regardless of the number it does print.
What does it mean if my report shows a result as ND?
ND means not detected, meaning the laboratory method used did not find the contaminant above its detection threshold, not necessarily that the concentration is exactly zero. Different methods have different detection limits, so ND on one report and ND on another do not automatically mean identical water if the underlying test methods differ in sensitivity.
Is a secondary standard violation actually dangerous?
No, not in the health sense. Secondary standards for iron, manganese, total dissolved solids, sulfate, chloride and pH are aesthetic guidelines covering staining, taste and appearance rather than enforceable health limits. A secondary violation is worth addressing for comfort and for protecting fixtures and appliances, but it is a different category of concern than a primary standard violation.
Why does the units column matter so much for nitrate?
Because nitrate can be reported as nitrate as nitrogen or as the nitrate ion, two different numbers for the same water, and the federal limit of 10 mg/L applies specifically to nitrate as N. Reading a nitrate ion result against the nitrogen based limit produces a false sense of security, which matters because nitrate is especially serious for infants.
Why does the PFAS section of my report keep changing over time?
The 2024 rule set enforceable limits of 4.0 ng/L for PFOA and PFOS, which is settled, but limits for several other PFAS compounds and a hazard index for mixtures have been subject to reconsideration since, with compliance timelines shifting. Check the current EPA rule directly for anything beyond PFOA and PFOS rather than relying on a table, including this one, to have caught up.
Get the complete water treatment shopping list
Every item in the starter, complete and premium systems for both city water and well water, with running totals, in one printable list. It opens with the test kit, because that is genuinely the first purchase. No charge.
One list, no sequence of daily emails, and you can leave at any time.
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.