Chromium-6 in Idaho Drinking Water
Ranked by max chromium-6 detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chromium-6 in Idaho: what the data shows
Idaho has 23 cities with chromium-6 data from the EPA's UCMR 3 program (2013–2015). Hexavalent chromium (Cr VI) was detected in 23 of those cities. There is currently no federal MCL for chromium-6 — California's 10 µg/L limit is used as a reference. The state average max detected level is 1.83 µg/L. Chromium-6 occurs naturally in some groundwater aquifers but also from industrial discharge, particularly from steel processing, chrome plating, and leather tanning. It is distinct from trivalent chromium (Cr III), which is an essential nutrient at low doses. The National Toxicology Program and IARC classify chromium-6 as a carcinogen via inhalation; the evidence for drinking water carcinogenicity is strong but regulatory action at the federal level remains pending as of 2026. Reverse osmosis systems effectively remove chromium-6 to near-undetectable levels.
Cities exceeding No federal MCL (CA: 10 µg/L)
Chromium-6 data across Idaho
Each dot is a city with UCMR 3 chromium-6 data. Detected cities are shown; there is no federal MCL — California's 10 µg/L limit is used as a reference. Size reflects population served.
Top 10 cities by chromium-6 level in Idaho
Highest Chromium-6 levels (µg/L)
All Idaho cities ranked by chromium-6 level
| # | City | Level | Level | Detected? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Chubbuck | 7.90 µg/L | Detected | 16 | C+ | |
| 2 | Nampa | 6.16 µg/L | Detected | 255 | F | |
| 3 | Caldwell | 6.09 µg/L | Detected | 226 | F | |
| 4 | Mountain Home | 3.09 µg/L | Detected | 55 | D | |
| 5 | Twin Falls | 3.01 µg/L | Detected | 71 | D+ | |
| 6 | Pocatello | 2.62 µg/L | Detected | 117 | F | |
| 7 | Boise | 2.40 µg/L | Detected | 218 | F | |
| 8 | Kuna | 2.10 µg/L | Detected | 98 | D | |
| 9 | Middleton | 1.70 µg/L | Detected | 64 | D+ | |
| 10 | Idaho Falls | 1.40 µg/L | Detected | 101 | D | |
| 11 | Rexburg | 1.10 µg/L | Detected | 83 | F | |
| 12 | Blackfoot | 0.79 µg/L | Detected | 85 | F | |
| 13 | Ammon | 0.77 µg/L | Detected | 52 | D+ | |
| 14 | Juliaetta | 0.76 µg/L | Detected | 22 | D | |
| 15 | Soda Springs | 0.44 µg/L | Detected | 20 | C+ | |
| 16 | Meridian | 0.40 µg/L | Detected | 34 | F | |
| 17 | Coeur D Alene | 0.31 µg/L | Detected | 125 | F | |
| 18 | Genesee | 0.30 µg/L | Detected | 8 | A- | |
| 19 | Post Falls | 0.27 µg/L | Detected | 56 | D | |
| 20 | Oakley | 0.23 µg/L | Detected | 37 | D | |
| 21 | Garden City | 0.18 µg/L | Detected | 12 | C- | |
| 22 | Lewiston | 0.13 µg/L | Detected | 91 | F | |
| 23 | Moscow | 0.04 µg/L | Detected | 20 | C- |
Frequently asked questions about chromium-6 in Idaho
Is chromium-6 in Idaho tap water dangerous?
Chromium-6 (hexavalent chromium) is a potential human carcinogen. There is currently no federal MCL — California's 10 µg/L limit is the most protective US standard. 23 cities in Idaho had detectable chromium-6 in UCMR 3 testing (2013–2015). Reverse osmosis is the most effective removal method.
Where does chromium-6 come from in Idaho water?
Chromium-6 enters water supplies from two main sources: natural weathering of chromium-containing rock formations (especially in the Southwest and parts of the Midwest) and industrial discharge from steel mills, chrome plating, and coal ash sites. Groundwater systems are more commonly affected by natural sources, while surface water systems near industrial areas face pollution-related risks.
How can I filter chromium-6 from my water in Idaho?
Reverse osmosis (RO) systems are the most effective, removing over 95% of chromium-6. Some high-quality activated alumina or anion exchange filters also provide significant reduction. Standard carbon filters and pitcher filters are generally NOT effective against chromium-6. Look for filters certified by NSF International against NSF/ANSI 58 (for RO systems).