We analyzed tap water quality data for hundreds of cities in New Hampshire 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EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels.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
Atkinson, New Hampshire
Atkinson has 10 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 Atkinson water report →Plainview, New Hampshire
Plainview has 9 contaminants exceeding EWG health guidelines out of 15 total detected, placing it among the most concerning water supplies analyzed.
See full Plainview water report →Merrimack, New Hampshire
Merrimack has 8 contaminants exceeding EWG health guidelines out of 18 total detected, placing it among the most concerning water supplies analyzed.
See full Merrimack water report →Jaffrey, New Hampshire
Jaffrey has 8 contaminants exceeding EWG health guidelines out of 13 total detected, placing it among the most concerning water supplies analyzed.
See full Jaffrey water report →West Stewartstown, New Hampshire
West Stewartstown has 8 contaminants exceeding EWG health guidelines out of 8 total detected, placing it among the most concerning water supplies analyzed.
See full West Stewartstown water report →Portsmouth, New Hampshire
Portsmouth has 6 contaminants exceeding EWG health guidelines out of 16 total detected, placing it among the most concerning water supplies analyzed.
See full Portsmouth water report →Monroe, New Hampshire
Monroe has 6 contaminants exceeding EWG health guidelines out of 14 total detected, placing it among the most concerning water supplies analyzed.
See full Monroe water report →Hudson, New Hampshire
Hudson has 5 contaminants exceeding EWG health guidelines out of 14 total detected, placing it among the most concerning water supplies analyzed.
See full Hudson water report →Nashua, New Hampshire
Nashua has 5 contaminants exceeding EWG health guidelines out of 13 total detected, placing it among the most concerning water supplies analyzed.
See full Nashua water report →Milford, New Hampshire
Milford has 5 contaminants exceeding EWG health guidelines out of 13 total detected, placing it among the most concerning water supplies analyzed.
See full Milford water report →Seabrook, New Hampshire
Seabrook has 5 contaminants exceeding EWG health guidelines out of 10 total detected, placing it among the most concerning water supplies analyzed.
See full Seabrook water report →Stratham, New Hampshire
Stratham has 5 contaminants exceeding EWG health guidelines out of 10 total detected, placing it among the most concerning water supplies analyzed.
See full Stratham water report →Rochester, New Hampshire
Rochester has 5 contaminants exceeding EWG health guidelines out of 9 total detected, placing it among the most concerning water supplies analyzed.
See full Rochester water report →Salem, New Hampshire
Salem has 5 contaminants exceeding EWG health guidelines out of 8 total detected, placing it among the most concerning water supplies analyzed.
See full Salem water report →Dover, New Hampshire
Dover has 4 contaminants exceeding EWG health guidelines out of 10 total detected, placing it among the most concerning water supplies analyzed.
See full Dover water report →Rye, New Hampshire
Rye has 4 contaminants exceeding EWG health guidelines out of 9 total detected, placing it among the most concerning water supplies analyzed.
See full Rye water report →Londonderry, New Hampshire
Londonderry has 4 contaminants exceeding EWG health guidelines out of 8 total detected, placing it among the most concerning water supplies analyzed.
See full Londonderry water report →Durham, New Hampshire
Durham has 4 contaminants exceeding EWG health guidelines out of 7 total detected, placing it among the most concerning water supplies analyzed.
See full Durham water report →East Kingston, New Hampshire
East Kingston has 4 contaminants exceeding EWG health guidelines out of 5 total detected, placing it among the most concerning water supplies analyzed.
See full East Kingston water report →Great Neck, New Hampshire
Great Neck has 4 contaminants exceeding EWG health guidelines out of 5 total detected, placing it among the most concerning water supplies analyzed.
See full Great Neck water report →Newfields, New Hampshire
Newfields has 4 contaminants exceeding EWG health guidelines out of 4 total detected, placing it among the most concerning water supplies analyzed.
See full Newfields water report →Exeter, New Hampshire
Exeter has 3 contaminants exceeding EWG health guidelines out of 12 total detected, placing it among the most concerning water supplies analyzed.
See full Exeter water report →Derry, New Hampshire
Derry has 3 contaminants exceeding EWG health guidelines out of 10 total detected, placing it among the most concerning water supplies analyzed.
See full Derry water report →Manchester, New Hampshire
Manchester has 3 contaminants exceeding EWG health guidelines out of 9 total detected, placing it among the most concerning water supplies analyzed.
See full Manchester water report →Hooksett, New Hampshire
Hooksett has 3 contaminants exceeding EWG health guidelines out of 9 total detected, placing it among the most concerning water supplies analyzed.
See full Hooksett water report →What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Perfluorooctanoic acid (PFOA), Perfluorooctane sulfonate (PFOS), Haloacetic acids (HAA9). 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, 130 contaminant readings exceed EWG health guidelines, but only 16 exceed EPA legal limits. This gap of 114 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 | Atkinson | NH | 19 | 10 | 0 | 2,838 |
| 2 | Plainview | NH | 15 | 9 | 2 | 123 |
| 3 | Merrimack | NH | 18 | 8 | 1 | 25,000 |
| 4 | Jaffrey | NH | 13 | 8 | 1 | 3,612 |
| 5 | West Stewartstown | NH | 8 | 8 | 0 | 0 |
| 6 | Portsmouth | NH | 16 | 6 | 0 | 33,000 |
| 7 | Monroe | NH | 14 | 6 | 0 | 23,000 |
| 8 | Hudson | NH | 14 | 5 | 1 | 16,100 |
| 9 | Nashua | NH | 13 | 5 | 1 | 87,682 |
| 10 | Milford | NH | 13 | 5 | 1 | 9,500 |
| 11 | Seabrook | NH | 10 | 5 | 0 | 14,000 |
| 12 | Stratham | NH | 10 | 5 | 3 | 150 |
| 13 | Rochester | NH | 9 | 5 | 0 | 25,000 |
| 14 | Salem | NH | 8 | 5 | 0 | 18,000 |
| 15 | Dover | NH | 10 | 4 | 0 | 28,000 |
| 16 | Rye | NH | 9 | 4 | 1 | 4,100 |
| 17 | Londonderry | NH | 8 | 4 | 2 | 875 |
| 18 | Durham | NH | 7 | 4 | 0 | 16,000 |
| 19 | East Kingston | NH | 5 | 4 | 0 | 72 |
| 20 | Great Neck | NH | 5 | 4 | 1 | 0 |
| 21 | Newfields | NH | 4 | 4 | 1 | 550 |
| 22 | Exeter | NH | 12 | 3 | 0 | 11,000 |
| 23 | Derry | NH | 10 | 3 | 0 | 15,145 |
| 24 | Manchester | NH | 9 | 3 | 1 | 133,000 |
| 25 | Hooksett | NH | 9 | 3 | 0 | 3,500 |
Frequently Asked Questions
What city has the worst tap water in New Hampshire?
Based on 2026 data, Atkinson, NH 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.
