Rockville Tap Water: City Plant or WSSC? (2026)

Who sends you your water bill: the City of Rockville, or WSSC Water?

That one detail decides which data applies to you. Rockville runs its own water system, but addresses just outside the city line are on the regional utility, so a Rockville mailing address can be on either of two suppliers. Both are legal to drink from. Neither has violations on file with the EPA. But what the public record says about each one is very different, and so are the questions worth asking.

This guide walks you through it in three steps: figure out your system, read the section that applies to you, then decide what, if anything, to do.

Step 1: Check your bill or your address

The simplest test is your water bill. It will come from either the City of Rockville or WSSC Water, the Washington Suburban Sanitary Commission.

• Inside the city limits: you are most likely on the city's Rockville Filtration Plant.
• Just outside the city line: you are most likely on WSSC Water, the regional utility that serves about 1.9 million people across Montgomery County and Prince George's County.

Our Rockville report covers ZIP codes 20850, 20851, 20852 and 20853, plus surrounding Rockville areas. A Rockville mailing address or ZIP code alone does not guarantee city water, so the bill is the surest check.

The two systems, side by side

	City plant	WSSC Water
People served	About 40,000	About 1.9 million
Connections	8,200	438,639
Source	Surface water	Potomac and Patuxent rivers
Federal PFAS test	Not in latest round	2 found, under EWG
Lead results	None published	1.05 ppb (90th pct.)
Violations	None on file	None on file

Sources: EPA Safe Drinking Water Information System; WSSC Water data via EWG.

If you're on Rockville city water

The Rockville Filtration Plant is a surface-water system supplying roughly 40,000 people through 8,200 connections. The EPA tracks it under PWSID MD0002717. The city treats its own water rather than buying it from a regional wholesaler, so what comes out of a city tap is the plant's work from start to finish.

What is known. The plant has no violations on file with the EPA. Like any surface-water system, it relies on heavy disinfection, and chlorine reacting with organic matter in the water is what creates trihalomethanes and haloacetic acids. Those byproducts form in the pipes after treatment, and they are the contaminants that most often sit above health guidelines in this region. Our Rockville data does not include byproduct averages for the city plant specifically, so we will not estimate them.

What is not known. Two gaps stand out:

• PFAS: the plant was not part of the EPA's most recent national PFAS monitoring round, so there is no federal PFAS result for it. Systems outside that sample are not required to test. Nobody has looked, which is not the same as nothing being there.
• Lead: no lead or copper results appear in the EPA's published record for this system. Lead usually comes from service lines and plumbing inside a building, so the answer can vary from one home to the next.

For city customers, then, the open question is less "how high is it?" and more "what is actually there?" A home test is the only way to fill that in for your own tap.

If you're on WSSC Water

Just outside the city line, the picture is better documented. WSSC Water meets every federal limit that applies to it. EWG's analysis of the utility's data shows four contaminants above its stricter health guidelines:

Contaminant	Found	EWG guideline	Over by
Haloacetic acids	49 ppb	0.1 ppb	490×
Trihalomethanes	66 ppb	0.15 ppb	440×
Chromium-6	0.13 ppb	0.02 ppb	6×
Arsenic	Detected	0.004 ppb	10×

Source: WSSC Water data via EWG. These apply to WSSC Water only, not to the city plant.

EWG links haloacetic acids to cancer and trihalomethanes to cancer and effects on fetal development. It links chromium-6 to stomach cancer, and arsenic to cancer, cardiovascular effects and developmental effects.

WSSC Water also has the data the city plant lacks. Its 90th percentile lead result was 1.05 ppb, well under the EPA action level, which is being lowered from 15 ppb to 10 ppb in November 2027, and about 5.3 times EWG's guideline of 0.2 ppb. EWG links lead to harm to the brain and nervous system. In the EPA's UCMR5 round (2023 to 2025), 2 PFAS compounds were found, PFPeA at 6.7 ppt and PFHxA at 4.8 ppt, both under EWG's standard and with no federal limit for either.

Why "legal" and "over EWG" can both be true

Federal limits are enforceable, and they factor in what treatment costs and what a utility can achieve. EWG's guidelines have no legal force. EWG describes them as "based only on protecting health and does not consider technical feasibility or the cost of water treatment." Being over one is not a violation. It is a more cautious reference point you can use to decide whether home filtration is worth it.

Your next move, whichever bill you get

City water: start with a test. With no published PFAS or lead results for the plant, your own tap is the clearest source of information you can get.

WSSC Water: the data is already public, and disinfection byproducts are the headline. If you want lower levels, under-sink reverse osmosis (RO) is a common way to reduce dissolved contaminants such as these. Carbon pitchers are a cheaper starting point, mostly for taste and odor, with results that vary by product.

The Sanavia Hydra is the tankless under-sink RO system we install throughout the area. In independent accredited lab testing of an Arlington, VA home's tap water, total trihalomethanes fell from 58 ppb to 2.79 ppb after the Hydra, a 95% reduction. The details are on our proof page.

Either way, a free water test is a good first step, and we can mail a kit anywhere in the U.S. For both systems in one place, see the full Rockville, MD water quality report.