Arsenic in Drinking Water in Wyoming
What residents of Wyoming 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, Wyoming Department of Environmental Quality, USGS · Last reviewed: 2025-01-01
Quick Answer
Is arsenic in drinking water a concern in Wyoming?
Yes. Wyoming has significant arsenic occurrence from volcanic and geothermal geology — the state sits atop the Yellowstone Hot Spot, one of the most geothermally active zones in North America. The Yellowstone region, Wind River Basin, and areas with volcanic and hydrothermal geology throughout western and central Wyoming have documented elevated arsenic in groundwater. Multiple Wyoming public water systems have required arsenic treatment.
Where does arsenic come from in Wyoming's water?
Volcanic and geothermal geology is the dominant arsenic source in Wyoming. The Yellowstone region and associated geothermal systems in northwestern Wyoming contribute arsenic to surface water and groundwater over a wide area. The Wind River Basin's alkaline volcanic chemistry creates conditions for elevated arsenic. Wyoming's extensive oil and gas development also means some produced water with arsenic can impact local water quality in energy development areas.
What should Wyoming residents know?
Wyoming communities in the Wind River Basin (Riverton, Lander area), Yellowstone region corridor, and Bighorn Basin relying on local groundwater face the most documented arsenic risk. Wyoming DEQ monitors public water systems and has documented multiple systems requiring treatment. Private well owners in volcanic and geothermal terrain throughout Wyoming should test.
Key Facts
| EPA MCL | 10 µg/L (10 ppb) |
| MCLG | Zero |
| Primary source | Yellowstone geothermal/volcanic geology; Wind River Basin alkaline volcanic aquifer chemistry; Bighorn Basin |
| Highest-risk region | Wind River Basin (Fremont County) — among highest naturally occurring arsenic concentrations in western U.S. |
| Tribal concern | Wind River Indian Reservation communities face jurisdiction and resource challenges for water quality |
| State regulator | Wyoming Department of Environmental Quality (DEQ) |
| Health effects | Bladder, lung, skin cancer; cardiovascular; diabetes risk |
| Effective treatment | Activated alumina or reverse osmosis — both in use at Wyoming community water systems |
Why Arsenic Matters in Wyoming
Wyoming's Yellowstone-influenced geology creates some of the highest naturally occurring arsenic concentrations in the western U.S. The Wind River Basin in particular has documented very high arsenic in some groundwater sources, with multiple communities requiring treatment. Wyoming's small population and vast geography mean many rural water systems serve tiny communities with limited technical and financial resources for arsenic treatment compliance. The state's energy sector adds potential non-geological arsenic concerns in oil and gas development areas.
Wyoming Arsenic Program
Wyoming DEQ monitors arsenic under federal SDWIS. Wyoming's volcanic geology in the Absaroka and Yellowstone volcanic fields produces naturally elevated arsenic in some groundwater. The Wyoming Basin and Great Divide Basin have documented arsenic in formation waters. Private well owners in volcanic terrain and near historic mining districts should test for arsenic.
Largest Wyoming Water Utilities
No arsenic violations on record in EPA SDWIS for Wyoming utilities in our database. Browse the largest utilities to review their full water quality record.
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
Wind River Basin communities (Riverton, Lander, Fremont County), Bighorn Basin communities (Worland, Thermopolis, Greybull), and rural private well users throughout Wyoming's volcanic and geothermal landscape face the highest arsenic risk. Wind River Indian Reservation communities face unique jurisdiction and resource challenges for water quality compliance.
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 Wyoming
- 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 Wyoming 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 Wyoming, 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
Wyoming State Overview
All utilities and water quality data
Wyoming 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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