We analyzed tap water quality data for hundreds of cities in Connecticut 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EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels.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
Mansfield, Connecticut
Mansfield has 18 contaminants exceeding EWG health guidelines out of 32 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Mansfield water report →Somers, Connecticut
Somers has 18 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 Somers water report →Enfield, Connecticut
Enfield has 18 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 Enfield water report →Simsbury, Connecticut
Simsbury has 18 contaminants exceeding EWG health guidelines out of 28 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Simsbury water report →Southington, Connecticut
Southington has 17 contaminants exceeding EWG health guidelines out of 34 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Southington water report →Avon, Connecticut
Avon has 17 contaminants exceeding EWG health guidelines out of 28 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Avon water report →Manchester, Connecticut
Manchester has 16 contaminants exceeding EWG health guidelines out of 40 detected — significantly above the national average. Multiple known carcinogens were found at levels of concern.
See full Manchester water report →East Windsor, Connecticut
East Windsor has 16 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 East Windsor water report →Plainville, Connecticut
Plainville has 16 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 Plainville water report →Farmington, Connecticut
Farmington has 16 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 Farmington water report →Meriden, Connecticut
Meriden 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.
See full Meriden water report →New Haven, Connecticut
New Haven 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 New Haven water report →Seymour, Connecticut
Seymour 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 Seymour water report →Derby, Connecticut
Derby 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 Derby water report →Oxford, Connecticut
Oxford 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 Oxford water report →Windham, Connecticut
Windham 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.
See full Windham water report →Cromwell, Connecticut
Cromwell 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 Cromwell water report →New Milford, Connecticut
New Milford 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 New Milford water report →Newtown, Connecticut
Newtown 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 Newtown water report →Bethel, Connecticut
Bethel 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 Bethel water report →Guilford, Connecticut
Guilford 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.
See full Guilford water report →Bridgeport, Connecticut
Bridgeport has 14 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 Bridgeport water report →East Lyme, Connecticut
East Lyme has 13 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 East Lyme water report →Greenwich, Connecticut
Greenwich 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 Greenwich water report →Putnam, Connecticut
Putnam has 13 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 Putnam water report →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, 387 contaminant readings exceed EWG health guidelines, but only 4 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 | Mansfield | CT | 32 | 18 | 0 | 27,199 |
| 2 | Somers | CT | 31 | 18 | 0 | 352 |
| 3 | Enfield | CT | 30 | 18 | 0 | 18,544 |
| 4 | Simsbury | CT | 28 | 18 | 0 | 14,691 |
| 5 | Southington | CT | 34 | 17 | 0 | 43,069 |
| 6 | Avon | CT | 28 | 17 | 0 | 11,590 |
| 7 | Manchester | CT | 40 | 16 | 1 | 51,198 |
| 8 | East Windsor | CT | 31 | 16 | 0 | 98,690 |
| 9 | Plainville | CT | 30 | 16 | 0 | 18,231 |
| 10 | Farmington | CT | 30 | 16 | 0 | 14,693 |
| 11 | Meriden | CT | 32 | 15 | 0 | 58,441 |
| 12 | New Haven | CT | 31 | 15 | 0 | 418,900 |
| 13 | Seymour | CT | 31 | 15 | 0 | 13,080 |
| 14 | Derby | CT | 31 | 15 | 0 | 1,101 |
| 15 | Oxford | CT | 31 | 15 | 0 | 120 |
| 16 | Windham | CT | 25 | 15 | 0 | 21,214 |
| 17 | Cromwell | CT | 23 | 15 | 0 | 14,316 |
| 18 | New Milford | CT | 23 | 15 | 0 | 12,659 |
| 19 | Newtown | CT | 23 | 15 | 2 | 6,054 |
| 20 | Bethel | CT | 22 | 15 | 1 | 9,507 |
| 21 | Guilford | CT | 29 | 14 | 0 | 33,975 |
| 22 | Bridgeport | CT | 27 | 14 | 0 | 351,756 |
| 23 | East Lyme | CT | 26 | 13 | 0 | 15,245 |
| 24 | Greenwich | CT | 21 | 13 | 0 | 53,297 |
| 25 | Putnam | CT | 17 | 13 | 0 | 7,300 |
Frequently Asked Questions
What city has the worst tap water in Connecticut?
Based on 2026 data, Mansfield, CT 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.
