A lab report can feel like the end of the question. You open the PDF, find the PFAS line, see a phrase like "not detected" or a small number with a less-than sign, and move on. That reflex makes sense, but a recent story is a good reason to slow down. In a report dated October 23, 2026, Circle of Blue covered a study suggesting PFAS contamination in drinking water may be underestimated. The headline points at a measurement problem, not a new alarm, and that distinction matters for anyone reading their own results.
The phrase in the coverage that deserves attention is the reference to PFAS concentrations that "fall below laboratory reporting limits." That wording describes the edge of what a lab can measure reliably. It does not describe the edge of what might be in your water. Keep those two ideas separate and the rest of this article becomes much easier to follow.
What a Reporting Limit Actually Is
A reporting limit is the lowest concentration a lab will report as a measured number using a specific method and instrument setup. Below that line, the lab cannot give a dependable figure. Depending on the lab and the report format, you may see "not detected," a value flagged as an estimate, or a less-than number that names the limit itself.
Reporting limits differ between laboratories and between analytical methods. Two results from the same tap can therefore look different on paper even when both labs did sound work. A difference in the printed number is not always a difference in the water.
Non-Detect Is Not the Same as Zero
A "not detected" result means the lab did not find the compound above its reporting limit, on that sample, using that method. It does not promise the compound is absent from your home. Sample collection, handling, timing, and the analytical method all shape what appears on the page, and a single result captures one moment at one point in the system.
This is the practical lesson the headline points toward. A clean line is useful information, but it is information about a specific test. It is not a permanent certificate for your plumbing, your well, or your city's supply.
Read Your Own Line in Four Steps
Start with the paperwork you already have. Work through the report in this order:
First, find the reporting limit or detection limit printed beside each PFAS compound. If the limit is missing, that is worth a question on its own.
Second, note how each value is marked. Look for flags that say a result is an estimate, that a value sits between the detection and reporting limits, or that nothing was found above the limit.
Third, check the sampling date and the sample location. The report should say whether the water came from a kitchen tap, a well head, or another point. A sample from a location that does not match your daily use answers a different question than the one you are asking.
Fourth, compare the limit to the goal you set for your home, rather than only reacting to the word "clear." If the reporting limit is higher than the level you care about, a non-detect tells you less than it appears to.
Questions to Ask the Lab or Your Utility
Paperwork answers some questions, and a short phone call can answer the rest. Consider asking:
What is the reporting limit for each PFAS compound on this report? Which analytical method did you use, and does it cover the compounds I am concerned about? Where exactly was the sample collected? If a result came back below the limit, is there a way to test with a lower reporting limit if I want more certainty?
Lab staff and utility representatives can usually explain the method in plain language. If they cannot, that is useful to know too.
When a Result Still Needs a Decision
If your report shows a detected result, or if you have a question the paperwork cannot settle, the next step belongs with people who can interpret it for your location. Your local water utility can explain its own monitoring program. Your state or local health department can tell you which guidance applies where you live. For questions about your own health, your doctor is the right person to ask.
A non-detect result is worth keeping in your records, but it works best alongside the rest of what you know about your water, including the source, any treatment you already use, and the results from other tests.
The Habit That Keeps the Warning Practical
Treat "not detected" as a statement about one test, read the reporting limit beside every number, and ask the lab what it cannot see. Those three habits cost little and turn a headline about underestimated contamination into something you can actually use at your own tap.