Well water in Jefferson County, Idaho
In Jefferson County, 16% of 63 tested well samples exceeded the EPA limit for total coliform (0 MPN/100mL), based on public data from Idaho statewide ground water quality monitoring (IDWR EDMS) and USGS Water Quality Portal.
209 individual samples from 63 wells, 1921 to 2025. Data refreshed September 9, 2026.
What individual samples found
Each row summarizes every public sample for that contaminant inside Jefferson 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 | |
|---|---|---|---|---|---|---|---|
| Total coliform 2011 to 2019 | 63 | 16% | 16% | 0 | 8.6 | 0 MPN/100mL EPA limit | |
| Arsenic 1990 to 2025 | 190 | 77% | 11% | 2 | 110 | 10 ug/L EPA limit | |
| Nitrate 1921 to 2025 | 148 | 89% | 5% | 0.84 | 16.3 | 10 mg/L EPA limit | |
| Uranium 1957 to 2025 | 140 | 86% | <1% | 2.01 | 33 | 30 ug/L EPA limit | |
| Fluoride 1990 to 2025 | 201 | 94% | 0% | 0.4 | 1.6 | 4 mg/L EPA limit | |
| Nitrite 1991 to 2011 | 102 | 9% | 0% | 0 | 0.02 | 1 mg/L EPA limit | |
| E. coli 1990 to 2008 | 92 | 0% | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Copper 1990 to 2020 | 87 | 34% | 0% | 0 | 0.013 | 1.3 mg/L EPA limit | |
| Lead 1990 to 2008 | 48 | 6% | 0% | 0 | 0.56 | 15 ug/L EPA limit | |
| Sodium 1977 to 2025 | 209 | 100% | no limit | 14 | 290 | 20 mg/L health guideline | |
| Chloride 1921 to 2025 | 208 | 100% | no limit | 12 | 470 | 250 mg/L nuisance level | |
| Iron 1956 to 2025 | 139 | 29% | no limit | 0 | 650 | 300 ug/L nuisance level | |
| Manganese 1990 to 2025 | 136 | 29% | no limit | 0 | 1,700 | 300 ug/L health guideline | |
| Radon 1989 to 1995 | 41 | 100% | no limit | 230 | 1,390 | 2,000 pCi/L health guideline |
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What this means
The contaminants most often above their limit here are total coliform (16% of 63 samples), arsenic (11% of 190 samples), and nitrate (5% of 148 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 Jefferson County
- Total coliform16% of 63 local samples were above the limit.
- Arsenic11% of 190 local samples were above the limit.
- Nitrate5% of 148 local samples were above the limit.
- Uranium<1% of 140 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 230 pCi/L.
- ChlorideDetected in 100% of local samples.
Treatment that fits the local profile
- Total coliform
- Inspect and repair the well cap and casing, then shock chlorinate and retest; UV disinfection whole-house; Chlorination system
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
- Uranium
- Point-of-use reverse osmosis; Anion exchange; Whole-house anion exchange
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
Get your Jefferson 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 Jefferson County.
Common questions
Is there arsenic in well water in Jefferson County?
Arsenic was detected in 77% of 190 public well samples in Jefferson County, and 11% 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 Jefferson County?
The median radon level across 41 public samples in Jefferson County was 230 pCi/L, with a high of 1,390 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Jefferson 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): 1,639 samples in Jefferson 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: 165 samples in Jefferson 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.