What are the PFAS numbers for each plant?

WSSC Water PFAS results for 2025 show a Potomac PFOS running average of about 1.1 ppt against a 4.0 ppt limit, with Patuxent running averages at 0.0 for regulated compounds.

By the Your Water Numbers desk, not WSSC Water · Updated November 2, 2026 · How we check

Reading this: Parts per trillion are small units, so one sample can move a lot. Compare the running average with the limit, and keep the single reading in view.

Did a 4.2 reading break the limit?

No, not on the way compliance is measured. WSSC Water’s PFAS results list one Potomac PFOS reading of 4.2 ppt in Q2 2025. That single sample is above 4.0, but compliance uses the running annual average, and that average read about 1.1 ppt at each of Q2, Q3 and Q4.

We show both because either figure alone misleads. The average alone hides a real high reading. The single reading alone suggests a breach that the rule doesn’t count as one.

How many compounds does the page compare?

Six. The utility compares six compounds on its results page. We’ve read and quoted the PFOS figure and the Patuxent averages. Open the page for the other lines rather than assuming they match.

PFAS are a family of long-lasting man-made chemicals, and PFOS is one of them.

Why does your plant matter here?

The figures differ by source. The Patuxent line shows 0.0 for regulated compounds in 2025, and the Potomac line carries the PFOS results above. About 75% of customers are on the Potomac plant.

So you need your plant before these numbers mean much. If you’re on a blend, you don’t get a single line here, and a guess isn’t worth much.

Are these numbers a test of your tap?

No. These are the utility’s plant-level results, and they say nothing specific about your home. They also stop at the period we read. A Q2 2026 page exists on the same site, and we haven’t read those figures, so check it for anything newer.

Nothing here tells you the water is safe for you personally. It tells you where the reported numbers stood against a limit. If you have a health question, ask your doctor or county health department.

Do you need a filter for PFAS?

We read only PFOS for Potomac and no 2026 quarter, so these figures can’t settle this for you. Read the latest results page first. On what we read, Patuxent’s regulated averages are 0.0 and Potomac’s PFOS average sits under the limit.

If you do want one, check the claim before you rely on it. Look for the unit’s listed certifications for PFAS and the replacement schedule. A reverse-osmosis unit is one type people use, and the link below is only one example.

A softener isn’t the same equipment. It’s aimed at hardness, and any filter for lead has its own certification to look for.

Where do these sit among the other lines?

The PFAS page is separate from the yearly report. Our tap report guide covers hardness, minerals, chlorine and nitrate, and none of those lines tell you about PFAS.

Questions on this page

Where each number comes from