Well water in Canyon County, Idaho
In Canyon County, 40% of 1,140 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.
1,530 individual samples from 617 wells, 1970 to 2025. Data refreshed September 9, 2026.
What individual samples found
Each row summarizes every public sample for that contaminant inside Canyon 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 1981 to 2025 | 1,140 | 92% | 40% | 7.05 | 150 | 10 ug/L EPA limit | |
| Uranium 1991 to 2025 | 361 | 88% | 17% | 9.8 | 120 | 30 ug/L EPA limit | |
| Total coliform 2003 to 2023 | 604 | 12% | 12% | 0 | 727 | 0 MPN/100mL EPA limit | |
| Nitrate 1970 to 2025 | 1,530 | 89% | 10% | 3.2 | 30.4 | 10 mg/L EPA limit | |
| E. coli 1990 to 2008 | 592 | <1% | <1% | 0 | 51 | 0 MPN/100mL EPA limit | |
| Fluoride 1990 to 2025 | 1,032 | 95% | <1% | 0.478 | 16 | 4 mg/L EPA limit | |
| Nitrite 1991 to 2023 | 1,262 | 13% | <1% | 0 | 3.3 | 1 mg/L EPA limit | |
| Copper 1990 to 2020 | 488 | 53% | 0% | 0.001 | 0.033 | 1.3 mg/L EPA limit | |
| Lead 1990 to 2008 | 260 | 7% | 0% | 0 | 4 | 15 ug/L EPA limit | |
| Chloride 1978 to 2025 | 1,070 | 100% | no limit | 13.6 | 203 | 250 mg/L nuisance level | |
| Sodium 1990 to 2025 | 801 | 100% | no limit | 51 | 206 | 20 mg/L health guideline | |
| Manganese 1990 to 2025 | 745 | 47% | no limit | 0 | 930 | 300 ug/L health guideline | |
| Iron 1975 to 2025 | 739 | 47% | no limit | 0 | 2,400 | 300 ug/L nuisance level | |
| Radon 1991 to 1999 | 106 | 100% | no limit | 480 | 3,620 | 2,000 pCi/L health guideline |
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What this means
The contaminants most often above their limit here are arsenic (40% of 1,140 samples), uranium (17% of 361 samples), and total coliform (12% of 604 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 is widespread in local groundwater. It is mainly a staining and taste problem, but high manganese also carries a health advisory for infants.
What to test for in Canyon County
- Arsenic40% of 1,140 local samples were above the limit.
- Uranium17% of 361 local samples were above the limit.
- Total coliform12% of 604 local samples were above the limit.
- Nitrate10% of 1,530 local samples were above the limit.
- E. coli<1% of 592 local samples were above the limit.
- Fluoride<1% of 1,032 local samples were above the limit.
- Nitrite<1% of 1,262 local samples were above the limit.
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
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
- E. coli
- Shock chlorination and fix the well cap or casing; UV disinfection whole-house; Chlorination system
Get your Canyon 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 Canyon County.
Common questions
Is there arsenic in well water in Canyon County?
Arsenic was detected in 92% of 1,140 public well samples in Canyon County, and 40% 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 Canyon County?
The median radon level across 106 public samples in Canyon County was 480 pCi/L, with a high of 3,620 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Canyon 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): 10,406 samples in Canyon 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: 324 samples in Canyon 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.