We analyzed tap water quality data for hundreds of cities in Iowa 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EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels.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
Waterloo, Iowa
Waterloo has 19 contaminants exceeding EWG health guidelines out of 33 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Elk Run Heights, Iowa
Elk Run Heights has 19 contaminants exceeding EWG health guidelines out of 33 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Sioux City, Iowa
Sioux City has 18 contaminants exceeding EWG health guidelines out of 40 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Hudson, Iowa
Hudson has 18 contaminants exceeding EWG health guidelines out of 37 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Ankeny, Iowa
Ankeny has 15 contaminants exceeding EWG health guidelines out of 33 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
West Burlington, Iowa
West Burlington has 15 contaminants exceeding EWG health guidelines out of 33 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Waukee, Iowa
Waukee has 15 contaminants exceeding EWG health guidelines out of 32 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Carter Lake, Iowa
Carter Lake 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.
Muscatine, Iowa
Muscatine has 15 contaminants exceeding EWG health guidelines out of 29 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Deep River, Iowa
Deep River has 15 contaminants exceeding EWG health guidelines out of 29 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Keokuk, Iowa
Keokuk has 15 contaminants exceeding EWG health guidelines out of 28 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Brooklyn, Iowa
Brooklyn has 15 contaminants exceeding EWG health guidelines out of 26 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Malcom, Iowa
Malcom has 15 contaminants exceeding EWG health guidelines out of 26 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Barnes City, Iowa
Barnes City has 15 contaminants exceeding EWG health guidelines out of 26 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Tama, Iowa
Tama has 15 contaminants exceeding EWG health guidelines out of 25 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Dysart, Iowa
Dysart has 15 contaminants exceeding EWG health guidelines out of 25 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Chelsea, Iowa
Chelsea has 15 contaminants exceeding EWG health guidelines out of 25 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Clutier, Iowa
Clutier has 15 contaminants exceeding EWG health guidelines out of 25 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Millersburg, Iowa
Millersburg has 15 contaminants exceeding EWG health guidelines out of 25 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Davenport, Iowa
Davenport 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.
Rock Valley, Iowa
Rock Valley has 15 contaminants exceeding EWG health guidelines out of 21 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
West Des Moines, Iowa
West Des Moines has 14 contaminants exceeding EWG health guidelines out of 37 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Oskaloosa, Iowa
Oskaloosa has 14 contaminants exceeding EWG health guidelines out of 30 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Lake Park, Iowa
Lake Park has 14 contaminants exceeding EWG health guidelines out of 29 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
Burlington, Iowa
Burlington has 14 contaminants exceeding EWG health guidelines out of 28 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Bromodichloromethane, Chloroform, Dibromochloromethane. 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, 385 contaminant readings exceed EWG health guidelines, but only 2 exceed EPA legal limits. This gap of 383 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 | Waterloo | IA | 33 | 19 | 0 | 69,504 |
| 2 | Elk Run Heights | IA | 33 | 19 | 0 | 1,069 |
| 3 | Sioux City | IA | 40 | 18 | 1 | 85,791 |
| 4 | Hudson | IA | 37 | 18 | 0 | 2,546 |
| 5 | Ankeny | IA | 33 | 15 | 0 | 68,090 |
| 6 | West Burlington | IA | 33 | 15 | 0 | 3,728 |
| 7 | Waukee | IA | 32 | 15 | 0 | 23,940 |
| 8 | Carter Lake | IA | 30 | 15 | 0 | 3,796 |
| 9 | Muscatine | IA | 29 | 15 | 0 | 23,797 |
| 10 | Deep River | IA | 29 | 15 | 0 | 249 |
| 11 | Keokuk | IA | 28 | 15 | 0 | 9,900 |
| 12 | Brooklyn | IA | 26 | 15 | 0 | 1,505 |
| 13 | Malcom | IA | 26 | 15 | 0 | 270 |
| 14 | Barnes City | IA | 26 | 15 | 0 | 0 |
| 15 | Tama | IA | 25 | 15 | 0 | 13,920 |
| 16 | Dysart | IA | 25 | 15 | 0 | 1,281 |
| 17 | Chelsea | IA | 25 | 15 | 0 | 229 |
| 18 | Clutier | IA | 25 | 15 | 0 | 213 |
| 19 | Millersburg | IA | 25 | 15 | 0 | 135 |
| 20 | Davenport | IA | 23 | 15 | 0 | 147,720 |
| 21 | Rock Valley | IA | 21 | 15 | 0 | 4,059 |
| 22 | West Des Moines | IA | 37 | 14 | 0 | 68,723 |
| 23 | Oskaloosa | IA | 30 | 14 | 0 | 11,558 |
| 24 | Lake Park | IA | 29 | 14 | 0 | 0 |
| 25 | Burlington | IA | 28 | 14 | 1 | 26,015 |
Frequently Asked Questions
What city has the worst tap water in Iowa?
Based on 2026 data, Waterloo, IA 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: 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.
