Arsenic in Drinking Water in Idaho
What residents of Idaho 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, Idaho Department of Environmental Quality, USGS · Last reviewed: 2025-01-01
Quick Answer
Is arsenic in drinking water a concern in Idaho?
Yes. Idaho has significant arsenic concerns due to its volcanic geology, geothermal activity, and extensive silver and phosphate mining history. The Snake River Plain — underlain by basalt and volcanic deposits — has documented elevated arsenic in some areas. The Blackfoot River watershed in southeastern Idaho, overlying one of the world's largest phosphate deposits, has documented naturally elevated arsenic from phosphate rock chemistry.
Where does arsenic come from in Idaho's water?
Three primary pathways exist in Idaho: volcanic and geothermal geology along the Snake River Plain, phosphate mining geology in southeastern Idaho (Bannock, Caribou, Power, and Bear Lake counties), and historic silver and gold mining in the Silver Valley and other central Idaho mining districts. Private wells and small water systems in these regions face elevated arsenic risk.
What should Idaho residents know?
Southeastern Idaho residents near the phosphate mining district (Pocatello, Soda Springs, and Blackfoot areas), communities in the Snake River Plain relying on shallow volcanic aquifers, and private well owners near historic mining districts in central Idaho should test for arsenic. Idaho DEQ monitors public water systems but private wells are unregulated.
Key Facts
| EPA MCL | 10 µg/L (10 ppb) |
| MCLG | Zero |
| Primary source | Phosphate mining geology (SE Idaho); volcanic/geothermal geology (Snake River Plain); historic mining (central Idaho) |
| Phosphate district concern | Bannock, Caribou, Power, Bear Lake counties — naturally elevated arsenic from phosphate rock chemistry |
| State regulator | Idaho Department of Environmental Quality (DEQ) |
| Health effects | Bladder, lung, skin cancer; cardiovascular; diabetes |
| Effective treatment | Reverse osmosis (NSF/ANSI 58) or activated alumina |
Why Arsenic Matters in Idaho
Idaho's arsenic profile reflects multiple geological and land-use factors. The southeastern Idaho phosphate belt — one of the world's richest phosphate deposits — naturally contains arsenic in the phosphate rock, which leaches into surface and groundwater. Historic gold and silver mining in central Idaho's Salmon River and Clearwater regions has left arsenic-bearing tailings. The Snake River Plain's volcanic aquifer, while a critical water supply, has localized areas of elevated arsenic from volcanic chemistry and geothermal input.
Idaho Arsenic Program
Idaho DEQ has an active arsenic compliance program as Idaho's volcanic Snake River Plain geology is one of the highest-arsenic geologies in the country. Many Idaho public water systems — particularly those drawing from Snake River Plain Aquifer — required treatment after the 2006 MCL tightening. Private well owners in the Snake River corridor face elevated arsenic risk and should test.
Idaho 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
Southeastern Idaho communities in Bannock, Caribou, Power, and Bear Lake counties (phosphate geology), central Idaho communities near mining districts, and Snake River Plain communities relying on volcanic aquifer groundwater face the most relevant arsenic risks.
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 Idaho
- 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 Idaho Department of Environmental Quality-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 Idaho, 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
Idaho State Overview
All utilities and water quality data
Idaho 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.
Find Your Utility
State Regulator
Idaho Department of Environmental Quality ↗