Well water in Oneida County, Idaho
In Oneida County, 4% of 57 tested well samples exceeded the EPA limit for nitrate (10 mg/L), based on public data from Idaho statewide ground water quality monitoring (IDWR EDMS) and USGS Water Quality Portal.
57 individual samples from 19 wells, 1991 to 2023. Data refreshed September 9, 2026.
What individual samples found
Each row summarizes every public sample for that contaminant inside Oneida 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 | |
|---|---|---|---|---|---|---|---|
| Nitrate 1991 to 2023 | 57 | 96% | 4% | 1.4 | 23.6 | 10 mg/L EPA limit | |
| Arsenic 1991 to 2023 | 50 | 92% | 2% | 3.05 | 19 | 10 ug/L EPA limit | |
| Fluoride 1991 to 2023 | 53 | 75% | 0% | 0.25 | 0.84 | 4 mg/L EPA limit | |
| Nitrite 1991 to 2013 | 42 | 5% | 0% | 0 | 0.01 | 1 mg/L EPA limit | |
| E. coli 1991 to 2008 | 35 | 0% | 0% | 0 | 0 | 0 MPN/100mL EPA limit | |
| Copper 1991 to 2019 | 33 | 70% | 0% | 0.002 | 0.025 | 1.3 mg/L EPA limit | |
| Lead 1991 to 2007 | 20 | 20% | 0% | 0 | 0.19 | 15 ug/L EPA limit | |
| Chloride 1991 to 2023 | 53 | 100% | no limit | 32.5 | 1,400 | 250 mg/L nuisance level | |
| Sodium 1991 to 2023 | 52 | 100% | no limit | 21.4 | 300 | 20 mg/L health guideline | |
| Iron 1991 to 2023 | 51 | 25% | no limit | 0 | 1,100 | 300 ug/L nuisance level | |
| Manganese 1991 to 2023 | 48 | 40% | no limit | 0 | 1,440 | 300 ug/L health guideline |
Sampled fewer than 10 times, too few to summarize: Uranium (8), Radon (4).
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What this means
The contaminants most often above their limit here are nitrate (4% of 57 samples) and arsenic (2% of 50 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 Oneida County
- Nitrate4% of 57 local samples were above the limit.
- Arsenic2% of 50 local samples were above the limit.
- Coliform bacteriaRecommended for every private well, every year.
- RadonMedian local reading is 525 pCi/L.
- ChlorideDetected in 100% of local samples.
- FluorideDetected in 75% of local samples.
- CopperDetected in 70% of local samples.
Treatment that fits the local profile
- Nitrate
- Point-of-use reverse osmosis; Anion exchange; Distillation
- Arsenic
- Point-of-use reverse osmosis; Adsorptive media (iron-based) whole-house; Anion exchange
- Fluoride
- Point-of-use reverse osmosis; Activated alumina; Distillation
- Copper
- Neutralizing filter to raise pH; Point-of-use reverse osmosis
- Chloride
- Point-of-use reverse osmosis; Distillation
Get your Oneida 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 Oneida County.
Common questions
Is there arsenic in well water in Oneida County?
Arsenic was detected in 92% of 50 public well samples in Oneida County, and 2% 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 Oneida County?
The median radon level across 4 public samples in Oneida County was 525 pCi/L, with a high of 610 pCi/L. New Hampshire recommends treatment above 2,000 pCi/L.
How often should I test a private well in Oneida 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): 493 samples in Oneida 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: 13 samples in Oneida 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.