We analyzed tap water quality data for hundreds of cities in Wyoming to identify the 25 with the most contaminants exceeding health guidelines. This ranking is based on 2026 data from the EPA and EWG databases.
While all public water systems must meet EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels. The cities below have the widest gap between what's in their water and what's considered safe by modern health standards.
Rankings at a Glance
Casper, Wyoming
Casper has 18 contaminants exceeding EWG health guidelines out of 27 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Casper water report →Laramie, Wyoming
Laramie has 17 contaminants exceeding EWG health guidelines out of 24 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Laramie water report →Farmington Hills, Wyoming
Farmington Hills has 17 contaminants exceeding EWG health guidelines out of 24 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Farmington Hills water report →Cheyenne, Wyoming
Cheyenne has 15 contaminants exceeding EWG health guidelines out of 23 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Cheyenne water report →Gillette, Wyoming
Gillette has 15 contaminants exceeding EWG health guidelines out of 23 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Gillette water report →F.e. Warren Afb, Wyoming
F.e. Warren Afb has 15 contaminants exceeding EWG health guidelines out of 23 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full F.e. Warren Afb water report →Rock Springs, Wyoming
Rock Springs has 15 contaminants exceeding EWG health guidelines out of 22 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Rock Springs water report →Green River, Wyoming
Green River has 15 contaminants exceeding EWG health guidelines out of 22 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Green River water report →Bar Nunn, Wyoming
Bar Nunn has 15 contaminants exceeding EWG health guidelines out of 19 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Bar Nunn water report →Midwest, Wyoming
Midwest has 15 contaminants exceeding EWG health guidelines out of 19 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Midwest water report →Edgerton, Wyoming
Edgerton has 15 contaminants exceeding EWG health guidelines out of 19 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Edgerton water report →Douglas, Wyoming
Douglas has 14 contaminants exceeding EWG health guidelines out of 19 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Douglas water report →Sacramento, Wyoming
Sacramento has 14 contaminants exceeding EWG health guidelines out of 19 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Sacramento water report →Fort Laramie, Wyoming
Fort Laramie has 14 contaminants exceeding EWG health guidelines out of 17 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Fort Laramie water report →Riverton, Wyoming
Riverton has 13 contaminants exceeding EWG health guidelines out of 33 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Riverton water report →Mills, Wyoming
Mills has 13 contaminants exceeding EWG health guidelines out of 18 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Mills water report →Burlington, Wyoming
Burlington has 13 contaminants exceeding EWG health guidelines out of 15 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Burlington water report →Hartville, Wyoming
Hartville has 13 contaminants exceeding EWG health guidelines out of 14 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Hartville water report →Fort Collins, Wyoming
Fort Collins has 12 contaminants exceeding EWG health guidelines out of 17 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Fort Collins water report →Wheatland, Wyoming
Wheatland has 12 contaminants exceeding EWG health guidelines out of 17 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Wheatland water report →Yellowstone National Park, Wyoming
Yellowstone National Park has 12 contaminants exceeding EWG health guidelines out of 16 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Yellowstone National Park water report →Torrington, Wyoming
Torrington has 12 contaminants exceeding EWG health guidelines out of 15 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Torrington water report →Sinclair, Wyoming
Sinclair has 12 contaminants exceeding EWG health guidelines out of 15 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Sinclair water report →Moorcroft, Wyoming
Moorcroft has 12 contaminants exceeding EWG health guidelines out of 14 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Moorcroft water report →Glendo, Wyoming
Glendo has 12 contaminants exceeding EWG health guidelines out of 14 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Glendo water report →What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Haloacetic acids (HAA5), Total trihalomethanes (TTHMs), Bromochloroacetic acid. These appear repeatedly across different water systems and regions.
Water quality varies significantly even within the same state, driven by local geology, agricultural activity, and industrial proximity.
Across all ranked cities, 350 contaminant readings exceed EWG health guidelines, but only 1 exceed EPA legal limits. This gap of 349 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 | Casper | WY | 27 | 18 | 0 | 59,000 |
| 2 | Laramie | WY | 24 | 17 | 0 | 30,899 |
| 3 | Farmington Hills | WY | 24 | 17 | 0 | 345 |
| 4 | Cheyenne | WY | 23 | 15 | 0 | 64,165 |
| 5 | Gillette | WY | 23 | 15 | 0 | 32,222 |
| 6 | F.e. Warren Afb | WY | 23 | 15 | 0 | 0 |
| 7 | Rock Springs | WY | 22 | 15 | 0 | 24,000 |
| 8 | Green River | WY | 22 | 15 | 0 | 10,500 |
| 9 | Bar Nunn | WY | 19 | 15 | 0 | 4,000 |
| 10 | Midwest | WY | 19 | 15 | 0 | 410 |
| 11 | Edgerton | WY | 19 | 15 | 0 | 195 |
| 12 | Douglas | WY | 19 | 14 | 0 | 6,400 |
| 13 | Sacramento | WY | 19 | 14 | 0 | 475 |
| 14 | Fort Laramie | WY | 17 | 14 | 0 | 0 |
| 15 | Riverton | WY | 33 | 13 | 0 | 10,330 |
| 16 | Mills | WY | 18 | 13 | 0 | 4,050 |
| 17 | Burlington | WY | 15 | 13 | 0 | 0 |
| 18 | Hartville | WY | 14 | 13 | 0 | 0 |
| 19 | Fort Collins | WY | 17 | 12 | 0 | 1,186 |
| 20 | Wheatland | WY | 17 | 12 | 0 | 0 |
| 21 | Yellowstone National Park | WY | 16 | 12 | 1 | 7,675 |
| 22 | Torrington | WY | 15 | 12 | 0 | 6,847 |
| 23 | Sinclair | WY | 15 | 12 | 0 | 0 |
| 24 | Moorcroft | WY | 14 | 12 | 0 | 1,009 |
| 25 | Glendo | WY | 14 | 12 | 0 | 0 |
Frequently Asked Questions
What city has the worst tap water in Wyoming?
Based on 2026 data, Casper, WY has the most contaminants exceeding EWG health guidelines among the cities we analyzed.
How are cities ranked in this report?
Cities are ranked by the number of contaminants exceeding EWG health guidelines. These guidelines are typically stricter than EPA legal limits and reflect current scientific research on safe exposure levels.
Is my tap water safe if my city isn't on this list?
Not necessarily. Even cities not on this list may have contaminants of concern. We recommend checking your specific water quality using our free water scan tool.
What's the best water filter for contaminated water?
A reverse osmosis (RO) system is the most effective for removing the widest range of contaminants. For whole-home protection, a combination of RO for drinking water and a whole-home filter for showers and baths is recommended.
Related Reports
Data sources: Environmental Working Group (EWG) Tap Water Database, U.S. EPA Safe Drinking Water Information System (SDWIS)
Last updated: March 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.
