We analyzed tap water quality data for hundreds of cities in Oregon 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EPA legal limits, many health experts — including the Environmental Working Group — argue that these legal limits are outdated and don't reflect current scientific understanding of safe exposure levels.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
Hermiston, Oregon
Hermiston has 8 contaminants exceeding EWG health guidelines out of 17 total detected, placing it among the most concerning water supplies analyzed.
See full Hermiston water report →Cornelius, Oregon
Cornelius has 8 contaminants exceeding EWG health guidelines out of 16 total detected, placing it among the most concerning water supplies analyzed.
See full Cornelius water report →Klamath Falls, Oregon
Klamath Falls has 8 contaminants exceeding EWG health guidelines out of 15 total detected, placing it among the most concerning water supplies analyzed.
See full Klamath Falls water report →Bend, Oregon
Bend has 7 contaminants exceeding EWG health guidelines out of 20 total detected, placing it among the most concerning water supplies analyzed.
See full Bend water report →Keizer, Oregon
Keizer has 7 contaminants exceeding EWG health guidelines out of 15 total detected, placing it among the most concerning water supplies analyzed.
See full Keizer water report →Wilsonville, Oregon
Wilsonville has 7 contaminants exceeding EWG health guidelines out of 13 total detected, placing it among the most concerning water supplies analyzed.
See full Wilsonville water report →Sherwood, Oregon
Sherwood has 7 contaminants exceeding EWG health guidelines out of 13 total detected, placing it among the most concerning water supplies analyzed.
See full Sherwood water report →Prineville, Oregon
Prineville has 7 contaminants exceeding EWG health guidelines out of 13 total detected, placing it among the most concerning water supplies analyzed.
See full Prineville water report →Pendleton, Oregon
Pendleton has 7 contaminants exceeding EWG health guidelines out of 12 total detected, placing it among the most concerning water supplies analyzed.
See full Pendleton water report →Tigard, Oregon
Tigard has 7 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full Tigard water report →Lake Oswego, Oregon
Lake Oswego has 7 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full Lake Oswego water report →Happy Valley, Oregon
Happy Valley has 6 contaminants exceeding EWG health guidelines out of 17 total detected, placing it among the most concerning water supplies analyzed.
See full Happy Valley water report →Portland, Oregon
Portland has 6 contaminants exceeding EWG health guidelines out of 15 total detected, placing it among the most concerning water supplies analyzed.
See full Portland water report →Troutdale, Oregon
Troutdale has 6 contaminants exceeding EWG health guidelines out of 15 total detected, placing it among the most concerning water supplies analyzed.
See full Troutdale water report →Redmond, Oregon
Redmond has 6 contaminants exceeding EWG health guidelines out of 14 total detected, placing it among the most concerning water supplies analyzed.
See full Redmond water report →Beaverton, Oregon
Beaverton has 6 contaminants exceeding EWG health guidelines out of 12 total detected, placing it among the most concerning water supplies analyzed.
See full Beaverton water report →Ontario, Oregon
Ontario has 6 contaminants exceeding EWG health guidelines out of 12 total detected, placing it among the most concerning water supplies analyzed.
See full Ontario water report →Hillsboro, Oregon
Hillsboro has 6 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full Hillsboro water report →Springfield, Oregon
Springfield has 6 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full Springfield water report →Milwaukie, Oregon
Milwaukie has 6 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full Milwaukie water report →Canby, Oregon
Canby has 6 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full Canby water report →St Helens, Oregon
St Helens has 6 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full St Helens water report →Gladstone, Oregon
Gladstone has 6 contaminants exceeding EWG health guidelines out of 11 total detected, placing it among the most concerning water supplies analyzed.
See full Gladstone water report →Coquille, Oregon
Coquille has 6 contaminants exceeding EWG health guidelines out of 9 total detected, placing it among the most concerning water supplies analyzed.
See full Coquille water report →Antelope, Oregon
Antelope has 6 contaminants exceeding EWG health guidelines out of 9 total detected, placing it among the most concerning water supplies analyzed.
See full Antelope water report →What We Found: Key Patterns
The most frequently detected contaminants exceeding health guidelines across these cities are Total trihalomethanes (TTHMs), Haloacetic acids (HAA5), 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, 164 contaminant readings exceed EWG health guidelines, but only 1 exceed EPA legal limits. This gap of 163 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 | Hermiston | OR | 17 | 8 | 0 | 19,696 |
| 2 | Cornelius | OR | 16 | 8 | 0 | 13,201 |
| 3 | Klamath Falls | OR | 15 | 8 | 0 | 40,475 |
| 4 | Bend | OR | 20 | 7 | 0 | 77,704 |
| 5 | Keizer | OR | 15 | 7 | 0 | 38,585 |
| 6 | Wilsonville | OR | 13 | 7 | 0 | 25,915 |
| 7 | Sherwood | OR | 13 | 7 | 0 | 19,885 |
| 8 | Prineville | OR | 13 | 7 | 0 | 11,000 |
| 9 | Pendleton | OR | 12 | 7 | 0 | 17,169 |
| 10 | Tigard | OR | 11 | 7 | 0 | 62,500 |
| 11 | Lake Oswego | OR | 11 | 7 | 0 | 40,000 |
| 12 | Happy Valley | OR | 17 | 6 | 0 | 50,003 |
| 13 | Portland | OR | 15 | 6 | 0 | 666,200 |
| 14 | Troutdale | OR | 15 | 6 | 0 | 16,185 |
| 15 | Redmond | OR | 14 | 6 | 0 | 37,566 |
| 16 | Beaverton | OR | 12 | 6 | 0 | 224,600 |
| 17 | Ontario | OR | 12 | 6 | 0 | 14,465 |
| 18 | Hillsboro | OR | 11 | 6 | 0 | 90,603 |
| 19 | Springfield | OR | 11 | 6 | 0 | 62,100 |
| 20 | Milwaukie | OR | 11 | 6 | 0 | 30,000 |
| 21 | Canby | OR | 11 | 6 | 0 | 18,754 |
| 22 | St Helens | OR | 11 | 6 | 0 | 13,410 |
| 23 | Gladstone | OR | 11 | 6 | 0 | 12,121 |
| 24 | Coquille | OR | 9 | 6 | 0 | 3,953 |
| 25 | Antelope | OR | 9 | 6 | 1 | 497 |
Frequently Asked Questions
What city has the worst tap water in Oregon?
Based on 2026 data, Hermiston, OR 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.
