Of the 153 US water systems in our data that serve 250,000 people or more, 24 receive an F grade in 2026. The lowest scores belong to Aqua PA Main System (43), San Jose Water (45), the City of Anaheim (45) and Miami-Dade’s main system (46). The most common reason is not illegal water. It is PFAS detections and contaminant levels well above health guidelines that are stricter than federal law. Eleven of the 24 had no EPA violation in any of the last 12 quarters.
That distinction matters. An F on TapWaterSafety is a signal to look closer and consider a filter matched to your water. It is not, by itself, a finding that your utility broke the law.
How this list was built
We used TapWaterSafety’s dataset of 1,000 utilities and kept systems that serve at least 250,000 people. That gives 153 large systems, of which 24 grade F (a score of 54 or lower). Together, the F-graded systems report serving about 15.1 million people.
EPA records are from EPA ECHO compliance records, checked October 7, 2026, covering the last 12 quarters. “Top concerns” are the items each utility page lists first; they flag things like any PFAS detection, contaminants far above EWG health guidelines, and recent violations. Our methodology page explains how scores and concerns are set.
The 24 lowest-graded large systems
California has the most systems on the list (9), followed by New Jersey (4). Twenty of the 24 draw surface water, three buy surface water from another utility, and one (Miami-Dade) uses groundwater.
The main concerns behind the low grades
Counting the top concerns listed for the 24 systems:
- PFAS detected: 23 of 24
- PFHxS (one PFAS chemical) significantly above health guideline: 16
- Haloacetic acids (HAA9) significantly above health guideline: 16
- Arsenic significantly above health guideline: 7 (Fresno, CWS - Bakersfield, Irvine Ranch, Truckee Meadows, Anaheim, Eastern Municipal and El Paso)
- HAA5 or total trihalomethanes above health guideline: several systems
“Above health guideline” means above EWG’s health guideline, which is usually far stricter than EPA’s legal limit. For example, EPA’s legal limit for arsenic is 10 ppb, while its health goal is zero. A system can meet the legal limit and still be flagged. Our arsenic guide and EWG vs. EPA explainer cover that gap.
On PFAS, EPA’s April 2024 rule set a limit of 4 parts per trillion each for PFOA and PFOS and 10 ppt for PFHxS, PFNA and GenX. In May 2026, EPA proposed keeping the PFOA and PFOS limits, rescinding the PFHxS, PFNA, GenX and mixture limits, and allowing some systems to request until 2031 to comply. As of October 2026, those were still proposals. See our PFAS rule explainer.
EPA records: what is actually on file
Most violations on this list are monitoring, testing or reporting violations. That means a required sample, report or notice was late or missing. It is not a finding that water exceeded a limit. A few systems do have health-based entries (an MCL or treatment technique category):
- Boston Water and Sewer Commission (MWRA): a Lead and Copper Rule treatment technique violation open since November 1, 2020, with violations in all 12 quarters. EPA’s record shows the system over the lead action level.
- MCWA (New York): a Lead and Copper Rule treatment technique violation open since January 1, 2025 (5 of 12 quarters).
- Mobile, Alabama: an open Stage 2 Disinfection Byproducts Rule MCL violation dated July 1, 2023, plus open monitoring violations under the Stage 1 and Stage 2 DBP rules.
- City of Laredo: an open Revised Total Coliform Rule MCL violation dated October 1, 2024, plus closed Lead and Copper Rule Revisions (treatment technique and reporting), surface water treatment monitoring, and public notice violations (6 of 12 quarters).
- San Jose Water: a Surface Water Treatment Rule treatment technique violation open since June 1, 2023.
- Aqua PA Main System: six closed entries, including a Ground Water Rule treatment technique violation (November 2024) and monitoring violations under the arsenic, inorganic chemicals, radionuclides and DBP rules.
Others had monitoring or reporting entries only: Philadelphia (a closed surface water treatment monitoring violation, 4 quarters), Passaic Valley (open lead and copper monitoring, synthetic organic chemicals monitoring and Consumer Confidence Report entries), Miami-Dade (open DBP and coliform monitoring), Greensboro (closed lead and copper monitoring), Anaheim (open DBP monitoring), El Paso (closed DBP monitoring) and NJ American Water - Coastal North (open lead and copper monitoring). None of the 24 is listed by EPA as a serious violator.
A utility may have resolved issues since our data was pulled. Check the EPA ECHO report linked on each utility page, and the utility’s latest Consumer Confidence Report, for current status.
What residents can do
1. Read your Consumer Confidence Report
Every community water system must send customers an annual water quality report by July 1. It lists detected contaminants, the legal limits, and any violations, with the utility’s explanation. Compare the levels for the contaminants above to the legal limit and the health goal. Our step-by-step guide on how to read your water quality report explains each column.
2. Match a filter to the concern
A filter is only useful if it is certified for the contaminant you care about. EPA recommends looking for certification to NSF/ANSI 53 or 58 for PFAS reduction, and checking the certifier’s listing. Note that current certifications focus on PFOA and PFOS, not every PFAS chemical.
- PFAS (most of this list): a filter certified for PFOA/PFOS reduction under NSF/ANSI 53 or 58, such as the Aquasana AQ-5300 under-sink carbon filter, or a reverse osmosis system like the AquaTru countertop or Aquasana OptimH2O under-sink unit. The Clearly Filtered pitcher is certified only for chlorine, taste and odor (NSF/ANSI 42); its PFAS figures come from the maker’s own lab testing. See our PFAS filter guide.
- Arsenic: reverse osmosis is the usual choice. Arsenic claims under NSF/ANSI 58 apply to specific arsenic forms and starting levels, so check the listing and your report. The AquaTru countertop RO unit, certified for arsenic V reduction, needs no plumbing.
- Disinfection byproducts (TTHMs, HAAs): activated carbon filters can reduce them; check the product’s certification listing for a TTHM reduction claim. See our TTHM and HAA5 guide.
- Lead (Boston, MCWA, or any older home): a filter certified to NSF/ANSI 53 for lead, plus testing at your own tap. Lead usually comes from service lines and home plumbing. See lead in tap water and how to find out if you have a lead pipe.
3. Test if your situation calls for it
If you have an older home, a baby on formula, or someone pregnant in the household, a test from a state-certified lab tells you what is coming out of your tap. Our guide on testing your tap water at home covers options. If you have health concerns, talk to your doctor.
4. Ask your utility
Utilities publish treatment plans, PFAS sampling results and lead service line inventories. Your utility’s water quality office can tell you what is planned and when.
Find your own system
Not in a big city? Most people are served by smaller systems. Search your ZIP code to see your utility’s grade, top concerns and EPA record, or compare with the top-graded big-city systems.
Sources
- TapWaterSafety methodology
- EPA ECHO: Enforcement and Compliance History Online
- EPA: National Primary Drinking Water Regulations
- EPA: PFAS National Primary Drinking Water Regulation
- EPA: Identifying drinking water filters certified to reduce PFAS
- EPA: Consumer Confidence Report information for consumers
- CDC: About choosing home water filters