A Zero on a Water Report Starts With a Lab Limit

Circle of Blue has published a report, carried from Inside Climate News and dated October 23, 2026, that asks whether PFAS contamination in drinking water may be underestimated. Its summary turns on a technical point that is easy to skip past: when PFAS concentrations in drinking water "fall below laboratory reporting limits," the figure on a lab sheet is a statement about what the instrument could see, not a complete statement about the water. The full piece is worth reading, and it is here: Circle of Blue's report on PFAS in drinking water. This explainer covers the lab vocabulary underneath that claim, so a Midwest reader can open a utility report without guessing what a zero means.

The terms on a lab sheet

A water lab works with at least two limits that matter to a household. The first is the method detection limit, the smallest amount an instrument can tell apart from background noise under a specific method. The second is the reporting limit, the lowest concentration the lab will put a number on in its report. A result between those two points is often flagged as an estimate, which tells you the lab saw something but did not want to stand behind an exact figure. Labs and state programs define these terms in their own ways, so the definitions printed on your own report are the ones to rely on.

Why "not detected" is not a verdict

When a result falls under the reporting limit, a report usually says "not detected," or it shows a "less than" value next to the compound. Those phrases describe the floor of the measurement on that day, with that method, in that lab. They do not say the water is free of the compound. A reader who sees "not detected" beside a contaminant has learned that the sample did not reach the lab's reporting floor. That is a useful fact, but it is a narrower one than a clean bill of health for the water, and it depends heavily on how low the floor was set.

The same table can look reassuring for two very different reasons. One row may reflect a sensitive method with a low limit that reached the water and found nothing. Another may reflect a higher limit that could never have shown a small amount. Without the limit printed next to the result, a reader cannot tell which situation the table describes.

Three questions for the utility office

Before you treat a zero as settled, ask the utility for the lab sheet behind the summary table, not only the one-page annual report. Ask four things: when the sample was collected, which lab analyzed it, what the reporting limit was for that compound, and whether the same compound was tested at every source or only at one. A utility that can answer these plainly has given you the means to judge its results for yourself. A utility that cannot locate the sheets has told you something about its records, and that is worth knowing too.

Read the gap as a question

The Circle of Blue headline uses the word underestimated, which means the reported picture may trail the actual one. For a household, the practical response is not alarm but a better question. If a town's report lists a contaminant as not detected, check whether the sampling covered the period you care about, whether the lab limit was low enough to answer the question you are asking, and whether the results were posted with dates. Those checks are records work. They take a phone call and an afternoon with the report in hand.

What to keep on file

Keep the annual report, the lab sheets, and the dates of any testing you ordered yourself. If you use a private well, the same logic applies to any test you order: write down the reporting limit before the sample goes out, so a result you get back cannot be read more generously than the lab allows. Questions about what a result means for your health belong with your doctor, and questions about treatment belong with your utility or a licensed water professional, not with a news explainer.

Some of the words on a water report will be unfamiliar, and that is fine. The rule that matters is simple: a lab can only report what its method can see. A zero on a water report is a statement about the test, and reading it that way is the first step toward understanding the water it describes.