Chlorate in Idaho Drinking Water
Ranked by max chlorate detected (µg/L) · UCMR 3 data (2013–2015) · Data from EPA SDWIS & UCMR
Chlorate in Idaho: what the data shows
Idaho has 14 cities with chlorate data from the EPA's UCMR 3 program (2013–2015). Chlorate exceeded the 210 µg/L EPA lifetime health advisory in 4 of those cities. The state average max detected level is 168.5 µg/L. Chlorate is a disinfection byproduct that forms when chlorine dioxide or hypochlorite solutions are used to disinfect drinking water. It is most common in systems that use chlorine dioxide for taste-and-odor control or that store hypochlorite for extended periods. There is no federal MCL — the EPA lifetime health advisory is 210 µg/L. Chlorate can interfere with thyroid function by blocking iodide uptake, an effect of particular concern for pregnant women, infants, and people with thyroid conditions. Reverse osmosis and ion exchange (anion-specific) are effective at removing chlorate; standard activated carbon filters provide only modest reduction.
Cities exceeding 210 µg/L EPA lifetime HA (no MCL)
Chlorate data across Idaho
Each dot is a city with UCMR 3 chlorate testing data. Cities where chlorate exceeds the 210 µg/L EPA lifetime health advisory are highlighted. Size reflects population served.
Top 10 cities by chlorate level in Idaho
Highest Chlorate levels (µg/L)
All Idaho cities ranked by chlorate level
| # | City | Level | Level | Over HA? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Genesee | 584.0 µg/L | Over HA | 8 | A- | |
| 2 | Garden City | 490.0 µg/L | Over HA | 12 | C- | |
| 3 | Boise | 310.0 µg/L | Over HA | 218 | F | |
| 4 | Meridian | 240.0 µg/L | Over HA | 34 | F | |
| 5 | Kuna | 170.0 µg/L | No | 98 | D | |
| 6 | Lewiston | 113.0 µg/L | No | 91 | F | |
| 7 | Twin Falls | 93.0 µg/L | No | 71 | D+ | |
| 8 | Mountain Home | 85.0 µg/L | No | 55 | D | |
| 9 | Caldwell | 82.0 µg/L | No | 226 | F | |
| 10 | Juliaetta | 75.0 µg/L | No | 22 | D | |
| 11 | Coeur D Alene | 37.0 µg/L | No | 125 | F | |
| 12 | Pocatello | 27.0 µg/L | No | 117 | F | |
| 13 | Soda Springs | 27.0 µg/L | No | 20 | C+ | |
| 14 | Nampa | 26.5 µg/L | No | 255 | F |
Frequently asked questions about chlorate in Idaho
Is chlorate in Idaho tap water dangerous?
Chlorate has no federal MCL. The EPA lifetime health advisory is 210 µg/L. 4 cities in Idaho exceed this level. Chlorate can interfere with thyroid iodide uptake, which is a particular concern for infants, pregnant women, and people with hypothyroidism.
Where does chlorate in Idaho water come from?
Chlorate is a byproduct of chlorine-based disinfectants — particularly chlorine dioxide and hypochlorite (bleach) solutions. Levels tend to be higher in systems that use chlorine dioxide for taste-and-odor treatment or store sodium hypochlorite at high concentrations or for long periods. Levels vary seasonally with disinfectant use.
How can I reduce chlorate exposure?
Reverse osmosis is the most effective home treatment for chlorate, typically removing 80–95%. Anion exchange systems also work but require regeneration. Standard activated carbon filters provide only limited chlorate reduction. Boiling does NOT remove chlorate.