Measuring "worst water quality" is harder than it sounds. A state can have many violations that are technical reporting failures, or few violations that include genuinely dangerous contaminant exceedances. We're using three measures that actually indicate risk: number of water systems exceeding EPA MCLs, PFAS detection rates, and the highest single contamination readings recorded.
The data below comes from EPA's UCMR 5 testing program (covering approximately 10,290 water systems, results through January 2026) and EWG's PFAS contamination database.
The Rankings: Systems Exceeding at Least One MCL
| State | Systems Exceeding MCL | Detection Rate | Max Level (ppt) |
|---|---|---|---|
| New Jersey | 152 | 81.5% | 210 |
| Massachusetts | 181 | 80.1% | 142 |
| New York | 98 | 50.0% | 165 |
| Michigan | 58 | 40.1% | 620 |
| California | 56 | 34.6% | 110 |
| Texas | 52 | 33.6% | 88 |
| Florida | 42 | 39.8% | 85 |
| North Carolina | 42 | 45.4% | 680 |
| Ohio | 36 | 40.7% | 98 |
| Illinois | 32 | 35.9% | 62 |
New Jersey and Massachusetts: The Northeast Problem
The Northeast has the worst PFAS contamination in the country, measured by both detection rates and system counts. This isn't surprising given the region's industrial history. New Jersey alone was home to dozens of chemical manufacturers through the 20th century. DuPont, Chemours (a DuPont spinoff), and dozens of smaller chemical plants discharged PFAS compounds into groundwater for decades before the chemicals were even named, let alone regulated.
Massachusetts faces a similar situation. The state has an 80.1% detection rate, meaning if you live in Massachusetts and drink municipal water, there's a roughly 4-in-5 chance your utility has detected PFAS. Whether it's above the 4 ppt MCL depends on your specific system and where you live relative to contamination sources.
Michigan: A Single Number
620 parts per trillion. That's the highest single PFAS reading in our dataset. It came from the Rockford area of Kent County, Michigan, downstream of a 3M facility that manufactured Scotchgard for decades. The contamination affected private wells throughout the area. The state of Michigan has been more aggressive than most in response, establishing its own MCLs for seven PFAS compounds and funding alternative water sources for affected communities, but the contamination itself is a fact that won't change quickly.
The town of Parchment, Michigan, population about 1,900, learned in 2018 that its water contained PFAS at levels many times above what was then considered safe. The discovery came not from routine testing but from a state-wide survey. Bottled water was distributed to residents for weeks.
North Carolina: The Cape Fear River
North Carolina's 680 ppt maximum reading is the highest in the country outside Michigan. It comes from systems near the Chemours Fayetteville Works plant, which discharges a PFAS compound called GenX (HFPO-DA) into the Cape Fear River. The river is the drinking water source for communities downstream, including Wilmington, a city of about 120,000 people.
Chemours, created when DuPont spun off its chemical division in 2015, inherited the PFAS liability. The Fayetteville Works plant has been the subject of regulatory action, consent orders, and litigation since 2017. Utilities downstream have installed treatment, but the contamination source remains active.
The West Virginia Context
West Virginia doesn't appear high in the rankings by raw numbers (12 systems exceeding MCL), but it warrants specific mention because it's home to one of the most famous PFAS contamination sites in the country: the DuPont Washington Works plant near Parkersburg. This is the site whose history was told in the film "Dark Waters." DuPont disposed of PFOA waste near the plant for decades, contaminating drinking water for communities along the Ohio River. The case resulted in $670 million in settlements. The legacy contamination affects water supplies in both West Virginia and Ohio (max 185 ppt in WV, 98 ppt in OH).
States That Are Actually Clean
The states with genuinely low PFAS contamination tend to share specific characteristics: limited industrial history, few military bases with documented AFFF use, and rural water systems drawing from relatively pristine sources.
- Arkansas: Max 3 ppt (below MCL), 18.4% detection rate, one of the lowest nationally
- North Dakota: Max 2 ppt, 11.8% detection rate, lowest in the dataset
- Hawaii: Max 3 ppt, 17.6% detection rate. Island geography limits some contamination vectors.
The Private Well Caveat
These rankings only cover public water systems. Private well users (approximately 43 million Americans) have no federal testing requirement. USGS research indicates that private wells in agricultural areas and near military bases have elevated PFAS contamination rates. If you're on a well in any high-contamination state, the public water data is not a proxy for what's in your well.
See full state rankings → | View PFAS tracker → | How to test your water →