What's in Potomac, MD tap water?
Potomac is served by WSSC Water from the river it shares a name with. The supply meets every federal limit, and still carries haloacetic acids and trihalomethanes at multiples of EWG's health-based guidelines — the gap between legal and safe that a reverse-osmosis system exists to close.
WSSC Water quality report, explained
What WSSC Water's own test results show for Potomac, compared with EWG's health guidelines. Every result here is within EPA legal limits.
Served by
WSSC Water
Potomac River + Patuxent River
11
over guideline
Zip codes covered: 20854, 20859 and surrounding Potomacareas. “× over” compares the detected level to EWG's health guideline, not the federal legal limit.
Measured by the EPA · Potomac, MD
Potomac, MD tap water is fully legal.
It is also 5.3× the health standard for lead.
Washington Suburban Sanitary Commission runs Potomac's water, drawing from surface water and supplying about 1,900,000 people through 438,639 service connections. A system that size runs a long distribution network, and water spends days in it between the plant and the tap.
Surface water needs heavy disinfection, and chlorine reacting with organic matter in the river is what creates trihalomethanes and haloacetic acids. Those are the contaminants that most often sit above health guidelines here, and they form in the pipes after treatment rather than at the plant.
Every federal limit that applies here is met. Those limits weigh what removal costs. EWG says its health standards are “based only on protecting health and does not consider technical feasibility or the cost of water treatment”. Here is how far apart the two are.
Harm to the brain and nervous system · EPA limit 10 ppb (action level, lowered from 15 ppb, in force November 2027)
Harm to fetal growth and child development · no federal limit exists
Harm to fetal growth and child development · no federal limit exists
The EPA's latest round found 2 PFAS compounds in this supply. Lead sampling put the ninetieth percentile at 1.05 ppb — meaning nine in ten homes tested below that, and one in ten above it. It has no violations on file.
Washington Suburban Sanitary Commission, on the EPA's record
- Source
- surface water
- Connections served
- 438,639
- People served
- 1,900,000
How this water is treated before it reaches you
Treatment makes water safe to distribute. It is not designed to remove PFAS, and chlorine-based disinfection creates byproducts of its own.
Levels: EPA Fifth Unregulated Contaminant Monitoring Rule (UCMR5, 2023–2025) for PFAS, and the Lead and Copper Rule 90th-percentile result for lead and copper — the highest reported for Washington Suburban Sanitary Commission. Health standards: EWG's published drinking water standards, updated February 2025. Levels vary by sampling point and date, and being above a health standard is not a legal violation.
The fix for Potomac water
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Reverse osmosis under your sink, for the 11 contaminants over EWG guidelines in water from WSSC Water.
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Potomac water quality FAQ
Is Potomac, MD tap water safe to drink?
Water from WSSC Water meets all federal EPA legal limits. However, independent EWG testing finds 11 contaminants above its stricter health-based guidelines, including haloacetic acids (HAA9) and haloacetic acids (HAA5). Legal compliance and health-optimal water are not the same thing.
What contaminants are in Potomac water?
The most notable contaminants above EWG health guidelines are haloacetic acids (HAA9), haloacetic acids (HAA5), total trihalomethanes (TTHMs), bromochloroacetic acid and 7 more. These are largely disinfection byproducts and trace metals common to the region's water sources.
Does a reverse osmosis system remove these contaminants?
Yes. A reverse osmosis system like the Sanavia Hydra uses a 0.0001-micron membrane plus multi-stage carbon filtration to reduce every contaminant class detected in Potomac water, at your tap, regardless of what the utility does upstream.
The contaminants flagged in Potomac water
Plain-English guides to what WSSC Watertesting turns up above EWG's health guidelines — what each one is, and what actually removes it.
Reverse osmosis in Potomac, MD
WSSC Water treats this water to the federal standard, yet the contaminants listed above still exceed EWG’s stricter health guidelines — Haloacetic acids (HAA9), Haloacetic acids (HAA5), Total trihalomethanes (TTHMs) and 8 more. Most of them either pass straight through treatment or form after the plant, in the pipes between it and the tap, which is why the fix has to be at the tap as well.
Trihalomethanes and haloacetic acids are not in the river — they form in the pipes, after treatment, when chlorine meets the organic matter it is there to deal with. That is why they are worst at the far end of a distribution network, and why filtering at the tap catches them where testing at the plant cannot.
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