Well water in Owyhee County, Idaho
In Owyhee County, 60% of 234 tested well samples exceeded the EPA limit for arsenic (10 ug/L), based on public data from Idaho statewide ground water quality monitoring (IDWR EDMS) and USGS Water Quality Portal.
266 individual samples from 98 wells, 1953 to 2025. Data refreshed September 9, 2026.
What individual samples found
Each row summarizes every public sample for that contaminant inside Owyhee County. Above limit means above the EPA maximum contaminant level; where EPA has no enforceable limit, the row shows a health guideline or nuisance level instead.
| Contaminant | Samples | Detected | Above limit | Median | Highest | Limit | |
|---|---|---|---|---|---|---|---|
| Arsenic 1991 to 2025 | 234 | 88% | 60% | 13.6 | 140 | 10 ug/L EPA limit | |
| Uranium 1954 to 2025 | 123 | 65% | 24% | 4.84 | 110 | 30 ug/L EPA limit | |
| Total coliform 2010 to 2022 | 120 | 18% | 18% | 0 | 579 | 0 MPN/100mL EPA limit | |
| Fluoride 1953 to 2025 | 176 | 96% | 18% | 0.9 | 20 | 4 mg/L EPA limit | |
| Nitrate 1978 to 2025 | 266 | 68% | 16% | 1.02 | 106 | 10 mg/L EPA limit | |
| Nitrite 1991 to 2022 | 206 | 8% | <1% | 0 | 8.02 | 1 mg/L EPA limit | |
| Copper 1991 to 2020 | 111 | 48% | 0% | 0 | 0.019 | 1.3 mg/L EPA limit | |
| E. coli 1991 to 2008 | 94 | 0% | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Lead 1991 to 2018 | 61 | 8% | 0% | 0 | 2 | 15 ug/L EPA limit | |
| Chloride 1980 to 2025 | 201 | 100% | no limit | 24 | 270 | 250 mg/L nuisance level | |
| Sodium 1964 to 2025 | 183 | 100% | no limit | 82 | 373 | 20 mg/L health guideline | |
| Manganese 1991 to 2025 | 166 | 83% | no limit | 72 | 6,090 | 300 ug/L health guideline | |
| Iron 1953 to 2025 | 165 | 72% | no limit | 32 | 5,000 | 300 ug/L nuisance level | |
| Radon 1990 to 1995 | 26 | 100% | no limit | 410 | 1,200 | 2,000 pCi/L health guideline |
Sampled fewer than 10 times, too few to summarize: Radium (226 + 228) (1).
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What this means
The contaminants most often above their limit here are arsenic (60% of 234 samples), uranium (24% of 123 samples), and total coliform (18% of 120 samples). A well next door can differ sharply from yours because bedrock fractures, well depth and plumbing all matter, so these rates describe the area, not your tap.
Chloride, Manganese, and Iron are widespread in local groundwater. They are mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Owyhee County
- Arsenic60% of 234 local samples were above the limit.
- Uranium24% of 123 local samples were above the limit.
- Total coliform18% of 120 local samples were above the limit.
- Fluoride18% of 176 local samples were above the limit.
- Nitrate16% of 266 local samples were above the limit.
- Nitrite<1% of 206 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
Treatment that fits the local profile
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Uranium
- Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
- Total coliform
- Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
Get your Owyhee County water tested at home
A licensed local water treatment company tests your tap water in your home, walks you through the numbers, and quotes treatment only if something needs fixing. Free, about 30 minutes, no obligation. Tell us what you need and we match you with a company that serves Owyhee County.
Common questions
Is there arsenic in well water in Owyhee County?
Arsenic was detected in 88% of 234 public well samples in Owyhee County, and 60% were above the EPA limit of 10 ug/L. Arsenic has no taste or smell; a lab test is the only way to know your level.
How high is radon in well water in Owyhee County?
The median radon level across 26 public samples in Owyhee County was 410 pCi/L, with a high of 1,200 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Owyhee County?
Test for bacteria and nitrate every year. Test once for arsenic, uranium, radon, fluoride, manganese and PFAS, then again every three to five years or after any change in taste, color, or plumbing.
Sources
- Idaho statewide ground water quality monitoring (IDWR EDMS): 2,060 samples in Owyhee County. Ground water quality results from the Idaho Department of Water Resources statewide monitoring program and partner agencies (ISDA, IDEQ, INL), EDMS bulk download. Retrieved September 9, 2026.
- USGS Water Quality Portal: 73 samples in Owyhee County. Data from the Water Quality Portal, a service of USGS, EPA and USDA; groundwater samples collected by USGS and cooperators. Retrieved September 3, 2026.
Non-detects count as samples and are treated as zero when computing medians. Exactly at the limit counts as not above it. A sample belongs to the town containing the well's reported coordinates.