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Not health advice. Contact your local water utility for concerns.
Data from EPA Water Quality Reports. For official information, contact your water utility or health department.
Real EPA measurements of arsenic for Idaho water systems — Six-Year Review compliance samples 2012–2019 (historical). Methodology
These cities have arsenic levels above 50% of the EPA limit but within compliance
| City | Level | % of Limit | Population |
|---|---|---|---|
| Twin Falls | 6.81 ug/L | 68.1% | 56,121 |
| Coeur d'Alene | 5.73 ug/L | 57.3% | 54,115 |
| Caldwell | 5.08 ug/L | 50.8% | 74,000 |
Every Idaho system with a arsenic result in EPA's data, sorted by level. Averages of 2012–2019 finished-water samples, non-detects counted as zero — historical, not today's tap.
| City | Level | Period | EPA Limit | % of Limit | Status |
|---|---|---|---|---|---|
| Twin FallsGrade B | 6.81 ug/LAverage of 120 samples | 2012–2019 | 10.00 ug/L | 68.1% | Warning |
| Coeur d'AleneGrade B | 5.73 ug/LAverage of 278 samples | 2012–2019 | 10.00 ug/L | 57.3% | Warning |
| CaldwellGrade A | 5.08 ug/LAverage of 32 samples | 2012–2019 | 10.00 ug/L | 50.8% | Warning |
| KunaGrade B | 4.87 ug/LAverage of 65 samples | 2012–2019 | 10.00 ug/L | 48.7% | Safe |
| NampaGrade B | 4.74 ug/LAverage of 29 samples | 2012–2019 | 10.00 ug/L | 47.4% | Safe |
| BoiseGrade B | 3.37 ug/LAverage of 306 samples | 2012–2019 | 10.00 ug/L | 33.7% | Safe |
| Mountain HomeGrade C | 2.68 ug/LAverage of 12 samples | 2012–2019 | 10.00 ug/L | 26.8% | Safe |
| ChubbuckGrade A | 2.67 ug/LAverage of 3 samples | 2012–2019 | 10.00 ug/L | 26.7% | Safe |
| EagleGrade A | 2.02 ug/LAverage of 6 samples | 2012–2019 | 10.00 ug/L | 20.2% | Safe |
| Post FallsGrade A | 1.91 ug/LAverage of 37 samples | 2012–2019 | 10.00 ug/L | 19.1% | Safe |
| RexburgGrade A | 1.60 ug/LAverage of 9 samples | 2012–2019 | 10.00 ug/L | 16.0% | Safe |
| PocatelloGrade B | 1.53 ug/LAverage of 17 samples | 2012–2019 | 10.00 ug/L | 15.3% | Safe |
| BlackfootGrade C | 1.25 ug/LAverage of 8 samples | 2012–2019 | 10.00 ug/L | 12.5% | Safe |
| Garden CityGrade B | 1.16 ug/LAverage of 13 samples | 2012–2019 | 10.00 ug/L | 11.6% | Safe |
| Idaho FallsGrade A | 1.07 ug/LAverage of 15 samples | 2012–2019 | 10.00 ug/L | 10.7% | Safe |
| AmmonGrade A | 1.01 ug/LAverage of 10 samples | 2012–2019 | 10.00 ug/L | 10.1% | Safe |
| LewistonGrade A | 0.833 ug/LAverage of 3 samples | 2012–2019 | 10.00 ug/L | 8.3% | Safe |
| MeridianGrade C | 0.717 ug/LAverage of 42 samples | 2012–2019 | 10.00 ug/L | 7.2% | Safe |
| MoscowGrade A | 0 ug/LAverage of 5 samples | 2012–2019 | 10.00 ug/L | 0.0% | Safe |
| JeromeGrade A | 0 ug/LAverage of 4 samples | 2012–2019 | 10.00 ug/L | 0.0% | Safe |
Arsenic is a known human carcinogen linked to cancers of the skin, bladder, lung, kidney, and liver. Long-term exposure can cause skin damage including color changes and lesions. Arsenic exposure is associated with cardiovascular disease, diabetes, and neurological effects. Studies have shown links between arsenic exposure and developmental effects in children, including reduced IQ and learning disabilities.
Erosion of natural deposits in the earth; runoff from orchards; discharge from glass and petroleum refineries
Based on our analysis of EPA Safe Drinking Water Information System (SDWIS) data and local water utility reports,arsenic has been detected in 20 Idaho water systems. The average level across all tested cities is 25% of the EPA Maximum Contaminant Level (MCL), with the highest detection at 68.1% of the limit.
The EPA set the arsenic MCL at 0.010 mg/L (10 ppb) in 2001. The EPA MCL for arsenic is 0.01 mg/L. This limit is set to protect public health based on available scientific evidence about the contaminant's health effects.
20 Idaho cities have arsenic detected in their water supply. All tested cities are within EPA safety limits.
Increased cancer risk (skin, bladder, lung), skin damage, cardiovascular disease, diabetes. The most vulnerable groups include children and people with cardiovascular conditions.
The most effective methods for removing arsenic include Reverse Osmosis, Adsorption Media (Iron-Based), Distillation. Look for filters certified by NSF/ANSI for arsenic reduction.
The EPA Maximum Contaminant Level (MCL) for arsenic is 0.01 mg/L.The EPA set the arsenic MCL at 0.010 mg/L (10 ppb) in 2001.
This page shows what Idaho utilities reported for arsenic. It cannot tell you what is coming out of your own tap: utility samples are taken across a whole system and averaged, levels vary by address and season, and anything picked up after the water leaves the main never appears in their report.
Home water test kitscheck your own tap before buying any filterRecommended filtration methods for arsenic removal:
Removes 90-95% of arsenic
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Paid links. We earn a commission if you buy, at no extra cost to you. Filters are matched to the removal methods listed above for arsenic.