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A New Study Says "Not Detected" Doesn't Mean Zero for PFAS. Here's How to Read Your Water Report.

When you look up your water utility's PFAS results, most of the lines say "not detected" or "below reporting limit." It's reassuring. But a study published October 23 in the journal Cell Reports Sustainability argues those lines are hiding a lot more of the so-called "forever chemicals" than...

Family First Water November 2, 2026

A New Study Says "Not Detected" Doesn't Mean Zero for PFAS. Here's How to Read Your Water Report.

When you look up your water utility's PFAS results, most of the lines say "not detected" or "below reporting limit." It's reassuring. But a study published October 23 in the journal Cell Reports Sustainability argues those lines are hiding a lot more of the so-called "forever chemicals" than most of us assume — likely more than half of what's actually in the water. Here's what the researchers found, why it matters in a Northern California home, and how to read your own report with a sharper eye.

What the study found

Researchers at Texas Christian University, led by environmental scientist Gehendra Kharel, went back through the EPA's latest national testing program for unregulated contaminants (known as UCMR 5). That dataset is huge: roughly 1.86 million individual PFAS test results from 9,991 community water systems across the country, covering 29 different PFAS compounds.

The catch is that about 98 percent of those results came back "below the minimum reporting level." The standard practice is to treat every one of those as zero. The TCU team instead used statistical modeling to estimate what those below-the-limit samples most likely contained, and the difference was striking. Counting the "not detected" results as zero captured only about 44 percent of the average combined PFAS concentration their model estimated. In plain terms, the reported numbers may be less than half the real picture.

Kharel put it simply to The New Lede: "Below the reporting limit does not mean zero." He was also careful to note that the finding is an estimate of how much PFAS is likely present, not a measurement, and the study doesn't say anyone's water is unsafe.

Why this matters at home

PFAS are a family of thousands of man-made chemicals used in nonstick pans, stain-resistant fabric, food packaging, and firefighting foam. They earned the "forever" nickname because they don't break down in the environment or in our bodies. The two best known, PFOA and PFOS, are the ones the EPA set drinking-water limits on in 2024 at 4 parts per trillion each — a tiny number that reflects how little it takes for these compounds to build up over years of daily exposure.

That's also why "below reporting limit" is a tricky phrase. A lab's reporting limit is the lowest amount it can reliably quantify, and for many PFAS that limit sits right around the level health agencies care about. Water can test "not detected" and still contain measurable PFAS just under the line. An analysis by the Environmental Working Group estimates that some 176 million Americans have drinking water with at least some PFAS in it.

The Northern California picture

California has done more PFAS testing than almost any state. A multiyear State Water Board study sampled 3,422 wells in 51 of the state's 58 counties and found PFOA or PFOS in about 17 percent of them — and the two usually showed up together. State scientists estimate those two compounds account for roughly 98 percent of the PFAS contamination found in California drinking-water sources.

The Sacramento region is part of that story. The City of Sacramento, which produces about 80 million gallons a day for 526,000 residents, found PFAS in some of its groundwater wells through state testing and in 2025 secured roughly $10.4 million from the 3M and DuPont settlements to help cover treatment costs. In Rancho Cordova, California American Water built a $1.28 million granular activated carbon system at its Nut Plains well after low levels of PFOA and PFOS turned up there — the only one of more than 60 wells in the area with detections. And just last week, Cal Water won planning approval to add activated carbon treatment at three of its Livermore stations for the same reason. Utilities are responding, but the treatment is happening well by well.

How to read your own report

Start with your utility's annual Consumer Confidence Report, which is mailed or posted every summer, and look for the PFAS section. Next to each "not detected" result, find the reporting limit (sometimes labeled DL, MRL, or RL). A result of "ND (4 ppt)" means the lab couldn't quantify anything below 4 parts per trillion — not that the water contained none. The lower the reporting limit, the more that "ND" actually tells you.

Then plug your zip code into the EWG Tap Water Database, which pulls together state and federal testing results and shows which PFAS have been detected in your system over time. For a reading at your own faucet, a certified lab test is the only way to know what's arriving after the water travels through miles of pipe and your home's plumbing.

If PFAS are a concern, the two home technologies designed to address them are activated carbon and reverse osmosis. Carbon is what utilities like Cal Water and Cal Am are installing at the well; reverse osmosis pushes water through a membrane fine enough to hold back dissolved contaminants like PFAS, nitrates, and lead, which is why it's the standard choice for drinking-water taps.

Curious what's in your water? Book a complimentary water test — about 30 minutes, no obligation.

Healthier water, healthier family.

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