Arsenic in Drinking Water in Oregon
What residents of Oregon need to know about arsenic in drinking water — including natural geological sources, private well risk, which utilities have documented violations, and how to remove arsenic from tap water.
Source: EPA SDWIS, Oregon Health Authority, USGS · Last reviewed: 2025-01-01
Quick Answer
Is arsenic in drinking water a concern in Oregon?
Yes. Oregon has significant arsenic occurrence due to its volcanic geology. The Cascade Range and associated volcanic plateau geology — which covers much of eastern and central Oregon — has documented elevated arsenic in groundwater from volcanic rock chemistry and geothermal activity. Willamette Valley communities relying on deeper groundwater wells can also encounter arsenic from volcanic ash and alluvial deposits.
Where does arsenic come from in Oregon's water?
Volcanic geology is the dominant arsenic pathway in Oregon. The High Lava Plains of eastern Oregon, the Cascade Volcanic Arc, and the Columbia River Basalt region all have documented elevated arsenic in groundwater. Central Oregon communities (Bend area), eastern Oregon communities on the High Lava Plains, and parts of the Willamette Valley drawing from deep volcanic aquifers face elevated risk.
What should Oregon residents know?
Communities in central and eastern Oregon relying on volcanic aquifer groundwater, and private well owners throughout Oregon's volcanic landscape, should test for arsenic. Oregon OHA monitors public water systems and has documented multiple systems requiring arsenic treatment. Oregon's large private well population in rural areas faces unregulated exposure.
Key Facts
| EPA MCL | 10 µg/L (10 ppb) |
| MCLG | Zero |
| Primary source | Cascade Volcanic Arc; High Lava Plains; Columbia River Basalt aquifer — volcanic rock chemistry |
| Highest-risk areas | Eastern Oregon and central Oregon volcanic terrain; Klamath Basin; Columbia Plateau communities |
| State regulator | Oregon Health Authority (OHA) |
| Health effects | Bladder, lung, skin cancer; cardiovascular; diabetes risk |
| Effective treatment | Reverse osmosis (NSF/ANSI 58) or activated alumina |
Why Arsenic Matters in Oregon
Oregon's Cascade Volcanic Arc and High Lava Plains create widespread arsenic occurrence in groundwater across a large portion of the state. The Columbia River Basalt — one of the world's largest flood basalt formations — which underlies much of eastern Oregon, contains arsenic that leaches into the regional basalt aquifer system. Communities in the Klamath Basin, Burns area, and other eastern Oregon population centers relying on local groundwater have documented arsenic concerns. Oregon OHA has been active in providing guidance and compliance assistance for affected small water systems.
Oregon Arsenic Program
Oregon OHA monitors arsenic under federal SDWIS and has documented elevated arsenic related to volcanic Columbia River Basalt geology. Eastern Oregon's volcanic geology produces naturally elevated arsenic in groundwater; multiple small water systems in eastern Oregon required treatment upgrades after 2006. Private well owners in eastern Oregon should test for arsenic as a baseline.
Oregon Utilities With Arsenic Violation Records
The utilities listed below have at least one arsenic violation on record in EPA's SDWIS database. Violations may be open or resolved — see individual utility pages for current status and risk level.
How Does Arsenic Get Into Drinking Water?
Arsenic in drinking water is almost always naturally occurring — it leaches from arsenic-bearing rocks and minerals into groundwater over time. New England granite, Southwest volcanic geology, and Upper Midwest glacial aquifers are the primary high-risk formations. It has no taste, odor, or color.
Full arsenic overview — geology maps, health effects, all 50 statesWho Should Pay Closest Attention
Eastern Oregon communities on the High Lava Plains and Columbia Plateau (Bend/Redmond area, Klamath Falls, Burns, La Grande, Pendleton), private well owners throughout Oregon's volcanic regions, and Willamette Valley users of deep volcanic aquifer wells should prioritize arsenic monitoring.
Private well owners near mining districts or agricultural areas
Residents in states with documented volcanic or geothermal geology
Long-term consumers of water from small groundwater systems
Households in homes built before 1960 with older well casings
Residents whose well water has never been tested for arsenic
Anyone living in a state where bedrock wells are common
How to Check Your Situation in Oregon
- 1
Identify your water source. If you use a public utility, use the ZIP lookup on this page to find your system and check its compliance record.
- 2
If on public water, review your utility's most recent Consumer Confidence Report (CCR) for arsenic monitoring data. The MCL is 10 ppb — your report should show recent test results.
- 3
If on a private well, order an arsenic test from a Oregon Health Authority-certified laboratory. A basic arsenic test costs $15–$40. The state agency website maintains a certified lab list.
- 4
Test your well at the tap — not just at the wellhead. The entire water distribution system within your home can affect water quality.
- 5
If your test shows arsenic above 5 ppb, install certified treatment immediately. If above 10 ppb, do not use the water for drinking or cooking until treatment is installed.
- 6
Retest after installing treatment to confirm it is working as certified. Replace filter media on the manufacturer's schedule — an exhausted filter may not perform as rated.
Treatment Options for Arsenic
Boiling does not remove arsenic — it concentrates it. Standard activated carbon filters (Brita, etc.) do not effectively remove arsenic. Certified treatment is required.
NSF/ANSI Standard 58 — Reverse Osmosis
RO systems certified to NSF/ANSI 58 remove 85–95% of arsenic. Under-sink installation. Most effective for removing multiple contaminants simultaneously. Replace membranes and pre-filters on schedule.
Activated Alumina Filters
Activated alumina is specifically designed for arsenic and fluoride removal. Point-of-use or whole-house options available. Must be certified by NSF International or WQA for arsenic reduction. Requires periodic media regeneration or replacement.
Iron/Manganese Oxidation Filters
Effective for arsenic in iron-rich well water, which is common in the Midwest and New England. Oxidation converts dissolved iron and arsenic to a form that can be filtered out. Best when arsenic is co-occurring with high iron levels.
What does NOT work for arsenic
Standard activated carbon filters (Brita, refrigerator filters, most pitcher filters) do NOT effectively remove arsenic. Boiling concentrates arsenic. Water softeners do not remove arsenic. Only use products with NSF certification specifically for arsenic reduction.
Take Action Now
If you use a private well in Oregon, test for arsenic — especially if you are in a region with granite, volcanic, or sedimentary geology. A basic arsenic test costs $15–$40 at a state-certified lab.
Public water users: check your utility's Consumer Confidence Report (CCR) for arsenic results. The EPA MCL is 10 ppb — any detection warrants attention.
If arsenic is detected above 10 ppb (or even below it, given MCLG is zero), install an NSF/ANSI 58-certified reverse osmosis system for drinking and cooking water.
Standard carbon filters do NOT remove arsenic — do not rely on a Brita or refrigerator filter for arsenic protection.
Frequently Asked Questions
Related Pages
Arsenic — National Overview
All U.S. utilities with arsenic records
Oregon State Overview
All utilities and water quality data
Oregon Well Water Guide
Testing, risks & certified labs for private wells
Reverse Osmosis Guide
Removes 85–95% of arsenic
Best Arsenic Filter Guide
What actually works (carbon doesn't)
PFAS in Drinking Water
The 'forever chemical' contamination overview
All Contaminants
Complete reference library
Data Sources & Provenance
All data on this page is sourced from official U.S. government or public datasets.
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