We analyzed tap water quality data for hundreds of cities in Missouri 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EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels.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
O Fallon, Missouri
O Fallon has 16 contaminants exceeding EWG health guidelines out of 36 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full O Fallon water report →Barnhart, Missouri
Barnhart has 15 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Barnhart water report →Arnold, Missouri
Arnold has 15 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Arnold water report →St Louis, Missouri
St Louis has 15 contaminants exceeding EWG health guidelines out of 30 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full St Louis water report →St Peters, Missouri
St Peters has 14 contaminants exceeding EWG health guidelines out of 35 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full St Peters water report →Chesterfield, Missouri
Chesterfield has 14 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Chesterfield water report →Kirkwood, Missouri
Kirkwood has 14 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Kirkwood water report →Arnonld, Missouri
Arnonld has 14 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Arnonld water report →Jefferson City, Missouri
Jefferson City has 14 contaminants exceeding EWG health guidelines out of 26 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Jefferson City water report →Webb City, Missouri
Webb City has 14 contaminants exceeding EWG health guidelines out of 26 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Webb City water report →St Charles, Missouri
St Charles has 13 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full St Charles water report →Bridgeton, Missouri
Bridgeton has 13 contaminants exceeding EWG health guidelines out of 31 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Bridgeton water report →Elsberry, Missouri
Elsberry has 13 contaminants exceeding EWG health guidelines out of 25 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Elsberry water report →Joplin, Missouri
Joplin has 13 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 Joplin water report →Neosho, Missouri
Neosho has 13 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 Neosho water report →Smithville, Missouri
Smithville has 13 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 Smithville water report →Garden City, Missouri
Garden City has 13 contaminants exceeding EWG health guidelines out of 21 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Garden City water report →Festus, Missouri
Festus has 13 contaminants exceeding EWG health guidelines out of 20 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Festus water report →Maryville, Missouri
Maryville has 13 contaminants exceeding EWG health guidelines out of 20 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Maryville water report →Mexico, Missouri
Mexico 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 Mexico water report →Sikeston, Missouri
Sikeston has 12 contaminants exceeding EWG health guidelines out of 26 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Sikeston water report →Kearney, Missouri
Kearney has 12 contaminants exceeding EWG health guidelines out of 26 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Kearney water report →Wentzville, Missouri
Wentzville has 12 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 Wentzville water report →Hannibal, Missouri
Hannibal has 12 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 Hannibal water report →Springfield, Missouri
Springfield has 12 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 Springfield water report →What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Total trihalomethanes (TTHMs), Bromodichloromethane, Chloroform. 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, 335 contaminant readings exceed EWG health guidelines, but only 1 exceed EPA legal limits. This gap of 334 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 | O Fallon | MO | 36 | 16 | 0 | 100,587 |
| 2 | Barnhart | MO | 31 | 15 | 0 | 36,000 |
| 3 | Arnold | MO | 31 | 15 | 0 | 20,000 |
| 4 | St Louis | MO | 30 | 15 | 0 | 304,709 |
| 5 | St Peters | MO | 35 | 14 | 0 | 52,575 |
| 6 | Chesterfield | MO | 31 | 14 | 0 | 1,100,000 |
| 7 | Kirkwood | MO | 31 | 14 | 0 | 28,000 |
| 8 | Arnonld | MO | 31 | 14 | 0 | 10,000 |
| 9 | Jefferson City | MO | 26 | 14 | 0 | 30,075 |
| 10 | Webb City | MO | 26 | 14 | 0 | 12,488 |
| 11 | St Charles | MO | 31 | 13 | 0 | 73,040 |
| 12 | Bridgeton | MO | 31 | 13 | 0 | 240 |
| 13 | Elsberry | MO | 25 | 13 | 1 | 2,051 |
| 14 | Joplin | MO | 22 | 13 | 0 | 73,728 |
| 15 | Neosho | MO | 22 | 13 | 0 | 12,157 |
| 16 | Smithville | MO | 22 | 13 | 0 | 10,290 |
| 17 | Garden City | MO | 21 | 13 | 0 | 1,590 |
| 18 | Festus | MO | 20 | 13 | 0 | 12,054 |
| 19 | Maryville | MO | 20 | 13 | 0 | 10,775 |
| 20 | Mexico | MO | 18 | 13 | 0 | 12,000 |
| 21 | Sikeston | MO | 26 | 12 | 0 | 16,291 |
| 22 | Kearney | MO | 26 | 12 | 0 | 11,500 |
| 23 | Wentzville | MO | 24 | 12 | 0 | 41,784 |
| 24 | Hannibal | MO | 23 | 12 | 0 | 17,108 |
| 25 | Springfield | MO | 22 | 12 | 0 | 172,025 |
Frequently Asked Questions
What city has the worst tap water in Missouri?
Based on 2026 data, O Fallon, MO 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: April 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.
