We analyzed tap water quality data for hundreds of cities across the United States to identify those with the highest levels of trihalomethane. This ranking is based on 2026 data from the EPA and EWG databases.
Trihalomethane is a contaminant of growing concern in drinking water. The cities below have the highest detected levels based on the most recent testing data available.
Rankings at a Glance
Marion, Louisiana
Marion has trihalomethane detected at 303.30 ppb. 18 total contaminants were found in the water supply.
Jones, Louisiana
Jones has trihalomethane detected at 283.80 ppb. 16 total contaminants were found in the water supply.
Paint Rock, Texas
Paint Rock has trihalomethane detected at 281.80 ppb. 23 total contaminants were found in the water supply.
Millersview, Texas
Millersview has trihalomethane detected at 271.40 ppb. 22 total contaminants were found in the water supply.
Sterlington, Louisiana
Sterlington has trihalomethane detected at 234.40 ppb. 14 total contaminants were found in the water supply.
Saline, Louisiana
Saline has trihalomethane detected at 228.40 ppb. 16 total contaminants were found in the water supply.
Joyce, Louisiana
Joyce has trihalomethane detected at 210.20 ppb. 18 total contaminants were found in the water supply.
Georgetown, Louisiana
Georgetown has trihalomethane detected at 205.90 ppb. 16 total contaminants were found in the water supply.
Wanette, Oklahoma
Wanette has trihalomethane detected at 186.30 ppb. 12 total contaminants were found in the water supply.
Asher, Oklahoma
Asher has trihalomethane detected at 176.80 ppb. 11 total contaminants were found in the water supply.
Rowena, Texas
Rowena has trihalomethane detected at 175.40 ppb. 30 total contaminants were found in the water supply.
Calvin, Louisiana
Calvin has trihalomethane detected at 171.50 ppb. 16 total contaminants were found in the water supply.
Maysville, Oklahoma
Maysville has trihalomethane detected at 171.40 ppb. 14 total contaminants were found in the water supply.
Ryan, Oklahoma
Ryan has trihalomethane detected at 171.20 ppb. 15 total contaminants were found in the water supply.
Tullos, Louisiana
Tullos has trihalomethane detected at 170.40 ppb. 16 total contaminants were found in the water supply.
Burnet, Texas
Burnet has trihalomethane detected at 166.70 ppb. 25 total contaminants were found in the water supply.
Mountain Park, Oklahoma
Mountain Park has trihalomethane detected at 162.20 ppb. 16 total contaminants were found in the water supply.
Mount Erie, Illinois
Mount Erie has trihalomethane detected at 156.50 ppb. 15 total contaminants were found in the water supply.
Indiahoma, Oklahoma
Indiahoma has trihalomethane detected at 151.10 ppb. 14 total contaminants were found in the water supply.
Rolling Fork, Mississippi
Rolling Fork has trihalomethane detected at 143.80 ppb. 7 total contaminants were found in the water supply.
Statenville, Georgia
Statenville has trihalomethane detected at 142.50 ppb. 10 total contaminants were found in the water supply.
Silverton, Texas
Silverton has trihalomethane detected at 140.40 ppb. 24 total contaminants were found in the water supply.
Provencal, Louisiana
Provencal has trihalomethane detected at 136.50 ppb. 13 total contaminants were found in the water supply.
Nome, Texas
Nome has trihalomethane detected at 132.20 ppb. 21 total contaminants were found in the water supply.
Waurika, Oklahoma
Waurika has trihalomethane detected at 130.30 ppb. 15 total contaminants were found in the water supply.
What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Haloacetic acids (HAA5), Total trihalomethanes (TTHMs), Bromodichloromethane. These appear repeatedly across different water systems and regions.
Geographically, the states most represented in this ranking are Louisiana (9), Oklahoma (7), Texas (6). Regional water sources, industrial activity, and agricultural runoff all contribute to local water quality variation.
Across all ranked cities, 264 contaminant readings exceed EWG health guidelines, but only 36 exceed EPA legal limits. This gap of 228 highlights how legal standards may not fully protect public health — EPA limits haven't been updated for many contaminants in decades.
Full Rankings Table
| Rank | City | State | Detected | Above Guidelines | Above Legal | People Served |
|---|---|---|---|---|---|---|
| 1 | Marion | LA | 18 | 11 | 1 | 1,635 |
| 2 | Jones | LA | 16 | 11 | 1 | 696 |
| 3 | Paint Rock | TX | 23 | 12 | 2 | 275 |
| 4 | Millersview | TX | 22 | 12 | 2 | 3,987 |
| 5 | Sterlington | LA | 14 | 11 | 1 | 1,095 |
| 6 | Saline | LA | 16 | 11 | 1 | 783 |
| 7 | Joyce | LA | 18 | 10 | 1 | 840 |
| 8 | Georgetown | LA | 16 | 10 | 1 | 1,872 |
| 9 | Wanette | OK | 12 | 8 | 2 | 402 |
| 10 | Asher | OK | 11 | 8 | 2 | 375 |
| 11 | Rowena | TX | 30 | 17 | 1 | 714 |
| 12 | Calvin | LA | 16 | 10 | 1 | 591 |
| 13 | Maysville | OK | 14 | 10 | 2 | 0 |
| 14 | Ryan | OK | 15 | 11 | 1 | 800 |
| 15 | Tullos | LA | 16 | 10 | 2 | 792 |
| 16 | Burnet | TX | 25 | 12 | 2 | 375 |
| 17 | Mountain Park | OK | 16 | 13 | 1 | 0 |
| 18 | Mount Erie | IL | 15 | 11 | 2 | 0 |
| 19 | Indiahoma | OK | 14 | 12 | 1 | 350 |
| 20 | Rolling Fork | MS | 7 | 3 | 1 | 1,808 |
| 21 | Statenville | GA | 10 | 9 | 2 | 0 |
| 22 | Silverton | TX | 24 | 13 | 1 | 597 |
| 23 | Provencal | LA | 13 | 8 | 2 | 1,032 |
| 24 | Nome | TX | 21 | 10 | 2 | 0 |
| 25 | Waurika | OK | 15 | 11 | 1 | 2,100 |
Frequently Asked Questions
What cities have the highest levels of trihalomethane?
Our analysis of 2026 data identified the cities with the highest detected levels of trihalomethane. See the full ranking above.
Is trihalomethane dangerous in drinking water?
Trihalomethane has known health risks at elevated levels. The EWG sets health guidelines that are often stricter than EPA legal limits to account for the latest research on long-term exposure.
How do I remove trihalomethane from my water?
Reverse osmosis (RO) systems are the most effective at removing a wide range of contaminants. Check the specific contaminant details for recommended filtration technology.
What is the EPA legal limit for trihalomethane?
EPA legal limits vary by contaminant and may differ from EWG health guidelines. See individual city reports for specific legal limit comparisons.
Related Reports
Data sources: Environmental Working Group (EWG) Tap Water Database, U.S. EPA Safe Drinking Water Information System (SDWIS)
Last updated: September 2026
Methodology: Contaminant levels are compared against both EPA legal limits (Maximum Contaminant Levels) and EWG health guidelines, which are often stricter and based on the latest scientific research.
