What's in Rockville, MD tap water?
Rockville treats its own water from the Potomac for most of the city, and addresses outside the city line are on WSSC Water. While fully EPA-compliant, its disinfection byproducts sit hundreds of times above EWG's stricter health guidelines, with nitrate and hexavalent chromium also over.
City of Rockville water quality report, explained
What City of Rockville's own test results show for Rockville, compared with EWG's health guidelines. Every result here is within EPA legal limits.
Surrounding county addresses
WSSC Water
Potomac River + Patuxent River
Rockville itself is on its own treatment plant — see above. Addresses just outside the city line are on WSSC Water.
11
over guideline
Zip codes covered: 20850, 20851, 20852, 20853 and surrounding Rockvilleareas. “× over” compares the detected level to EWG's health guideline, not the federal legal limit.
Measured by the EPA · Rockville, MD
Rockville, MD runs its own water system — and it has not been tested for PFAS.
Rockville is served by Rockville Filtration Plant, a surface-water system supplying roughly 40,000 people. It treats its own water rather than buying it from a regional wholesaler, so what comes out of the tap is its work end to end.
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.
Rockville Filtration Plant was not part of the EPA's most recent national PFAS monitoring round, so there is no federal PFAS result for it. Nobody has looked, which is not the same as nothing being there. No lead or copper results appear in EPA's published record for this system. It has no violations on file.
Rockville Filtration Plant, on the EPA's record
- Source
- surface water
- Connections served
- 8,200
- People served
- 40,000
Source: EPA Safe Drinking Water Information System record for Rockville Filtration Plant (PWSID MD0002717). Systems outside the UCMR5 sample are not required to test for PFAS.
9 contaminants above EWG's health guidelines
Everything EWG found above its guideline in Rockville's water, from testing in 2014-2023. A level can be under the legal limit and still be listed here: EWG's guidelines are set to protect health, not to be easy to meet.
| Contaminant | In this water | EWG guideline | Times over |
|---|---|---|---|
| Haloacetic acids (HAA9) | 26.6 ppb | 0.06 ppb | 443× |
| Total trihalomethanes (TTHMs) | 41.5 ppb | 0.15 ppb | 277× |
| Haloacetic acids (HAA5) | 20.1 ppb | 0.1 ppb | 201× |
| Bromodichloromethane | 2.79 ppb | 0.06 ppb | 46× |
| Dibromochloromethane | 2.40 ppb | 0.1 ppb | 24× |
| Nitrate and nitrite | 1.47 ppm | 0.14 ppm | 11× |
| Nitrate | 1.30 ppm | 0.14 ppm | 9.3× |
| Chloroform | 2.21 ppb | 0.4 ppb | 5.5× |
| Chromium (hexavalent) | 0.0899 ppb | 0.02 ppb | 4.5× |
Source: EWG Tap Water Database, City of Rockville (MD0150003).
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Rockville water quality FAQ
Is Rockville, MD tap water safe to drink?
Water from City of Rockville meets all federal EPA legal limits. However, independent EWG testing finds 9 contaminants above its stricter health-based guidelines, including haloacetic acids (HAA9) and total trihalomethanes (TTHMs). Legal compliance and health-optimal water are not the same thing.
What contaminants are in Rockville water?
The most notable contaminants above EWG health guidelines are haloacetic acids (HAA9), total trihalomethanes (TTHMs), haloacetic acids (HAA5), bromodichloromethane and 5 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 Rockville water, at your tap, regardless of what the utility does upstream.
The contaminants flagged in Rockville 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 Rockville, 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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