Wells & Rural
A Zero Is Not a Clean Bill: Keep the Reporting Limit With Your Well Records
A well report that says not detected tells you what the lab could measure, so the file needs the reporting limit kept beside the result.
A private well report can look finished the moment it arrives. A line says "not detected," a box is checked, and the sheet goes into a folder with the warranty for the pump. For PFAS, that one line may carry less information than it appears to. A Circle of Blue report on a new study, dated October 23, 2026, raises the question of whether PFAS in drinking water may be underestimated. The summary of that piece notes that "When PFAS concentrations in drinking water fall below laboratory reporting limits," the results are harder to read than a simple yes or no. Circle of Blue is the outlet, and the story itself is the source for that finding.
What a lab line actually says
Every analytical method has a reporting limit, which is the lowest concentration a laboratory will report as a number for that method under its own quality rules. Some labs also track a lower detection level, the point where a signal can be distinguished from background noise. A result below the reporting limit is usually written as a non-detect, a less-than figure, or a flagged value. That wording describes what the instrument and method could confirm on that day. It does not certify that the compound is absent from the water.
This matters most for a well owner because there is no utility report to fall back on. A city customer may see a annual summary of many samples. A household with its own well usually has one sample, taken on one day, from one tap, and that sample becomes the entire record. If the result sits under a reporting limit, the home's file reads as clean even when the honest answer is that the test could not see the level in question.
What to keep in the well file
Treat the lab report as a set of parts rather than a single verdict. Keep the full report, not only the summary page, and make sure it includes these items:
The name of the laboratory and the analytical method, which is usually given as a method number. The reporting limit for each compound tested, printed next to each result. The date the sample was collected and the date it was analyzed, since holding times can matter. The sampling point, such as a kitchen cold tap, an outdoor spigot, or a point before or after a treatment unit. Any note about the well, including whether the pump had been running or the water had been sitting in the lines overnight.
If your sample was taken after a filter, record that fact in plain words on the same page. A treated sample describes the water at that tap with that filter in place. It does not describe the water entering the house. A separate note in the folder prevents a future reader from mixing the two.
When to call the lab
Ask the laboratory for the reporting limit in writing if it is missing from your copy. Ask the method name and whether the lab used a version that targets the compounds you care about. Those are ordinary questions, and a lab that runs environmental testing will know how to answer them. If you plan to compare a new test with an older one, ask whether the reporting limit changed between the two, because a lower limit can reveal a number that an older test could not show.
Ask, too, whether a retest makes sense on a different schedule. A single sample is a snapshot of one moment. Water chemistry in a private well can shift with rainfall, with pump cycling, and with changes in the aquifer, and the study coverage is a reminder that one clean line does not close the question for good.
Read the study for its scope
The new research discussed in the Circle of Blue report points to a possibility that testers may be missing some contamination when results fall near or below their limits. That is a claim about measurement, and it should be read as a prompt to check your own file rather than as a verdict on any particular well. Nothing in that reporting tells a household what its water contains. It tells a household what to look for when the paperwork says less than the water might.
For rural readers, the practical lesson is simple. Keep the reporting limit with the result, record where and when the sample was taken, and note whether a treatment unit stood between the tap and the lab. A well file is only as useful as the context attached to each number, and a non-detect without its limit is a sentence without its subject.