Copper in Idaho Drinking Water
Ranked by 90th percentile copper level (mg/L) · Data from EPA SDWIS & UCMR
Copper in Idaho: what the data shows
Idaho has 35 cities with copper monitoring data. The state average 90th percentile copper level is 3.611 mg/L, compared to 28.808 mg/L nationally — better than the national average. 35 cities exceed the EPA action level of 1.3 mg/L. Copper in drinking water typically comes from corrosion of copper pipes and plumbing fixtures, particularly in older homes. The EPA action level of 1.3 mg/L is the 90th percentile threshold — if more than 10% of tap samples exceed it, utilities must take corrective action including adjusting water chemistry to reduce corrosivity. Short-term copper exposure above the action level can cause gastrointestinal distress. Long-term exposure at elevated levels is associated with liver and kidney damage. Flushing your tap for 30 seconds before use and using an NSF 53-certified filter can reduce copper exposure.
Cities exceeding 1.3 mg/L EPA Action Level
Copper data across Idaho
Each dot is a city, colored by overall water quality grade. Cities with copper levels above the 1.3 mg/L EPA action level are highlighted. Size reflects population served.
Top 10 cities by copper level in Idaho
Highest Copper levels (mg/L)
All Idaho cities ranked by copper level
| # | City | Level | Level | Exceeds? | Violations | Grade |
|---|---|---|---|---|---|---|
| 1 | Nampa | 63.000 mg/L | Yes | 255 | F | |
| 2 | Salmon | 3.869 mg/L | Yes | 43 | D | |
| 3 | Mccall | 3.580 mg/L | Yes | 19 | F | |
| 4 | Spirit Lake | 3.550 mg/L | Yes | 26 | D+ | |
| 5 | Clark Fork | 3.210 mg/L | Yes | 3 | A- | |
| 6 | Preston | 2.202 mg/L | Yes | 82 | F | |
| 7 | Orofino | 1.990 mg/L | Yes | 107 | D | |
| 8 | Pinehurst | 1.990 mg/L | Yes | 0 | A- | |
| 9 | Plummer | 1.880 mg/L | Yes | 24 | F | |
| 10 | Coolin | 1.870 mg/L | Yes | 2 | B+ | |
| 11 | Moyie Springs | 1.800 mg/L | Yes | 18 | B | |
| 12 | Gooding | 1.770 mg/L | Yes | 13 | B+ | |
| 13 | Inkom | 1.755 mg/L | Yes | 13 | B+ | |
| 14 | St Maries | 1.740 mg/L | Yes | 17 | B- | |
| 15 | Grace | 1.740 mg/L | Yes | 14 | B- | |
| 16 | Caldwell | 1.700 mg/L | Yes | 226 | F | |
| 17 | Eagle | 1.680 mg/L | Yes | 52 | F | |
| 18 | Kellogg | 1.660 mg/L | Yes | 90 | C+ | |
| 19 | Coeur D'Alene | 1.630 mg/L | Yes | 87 | D | |
| 20 | Boise | 1.600 mg/L | Yes | 218 | F | |
| 21 | Hayden | 1.590 mg/L | Yes | 56 | D | |
| 22 | Post Falls | 1.580 mg/L | Yes | 56 | D | |
| 23 | Pocatello | 1.570 mg/L | Yes | 117 | F | |
| 24 | Coeur D Alene | 1.570 mg/L | Yes | 125 | F | |
| 25 | Cascade | 1.560 mg/L | Yes | 5 | B+ | |
| 26 | Rexburg | 1.519 mg/L | Yes | 83 | F | |
| 27 | Kamiah | 1.500 mg/L | Yes | 127 | D | |
| 28 | Kingston | 1.480 mg/L | Yes | 16 | A- | |
| 29 | Uconn | 1.440 mg/L | Yes | 0 | A | |
| 30 | Garden Valley | 1.410 mg/L | Yes | 109 | D | |
| 31 | Blackfoot | 1.405 mg/L | Yes | 85 | F | |
| 32 | Bonners Ferry | 1.400 mg/L | Yes | 516 | D | |
| 33 | Idaho City | 1.400 mg/L | Yes | 20 | B- | |
| 34 | Sandpoint | 1.390 mg/L | Yes | 328 | F | |
| 35 | Rathdrum | 1.369 mg/L | Yes | 79 | D |
Frequently asked questions about copper in Idaho
Is copper in Idaho drinking water safe?
35 cities in Idaho exceed the EPA action level of 1.3 mg/L for copper. The state average is 3.611 mg/L. Copper levels are highest in homes with copper plumbing, particularly when water sits in pipes overnight. Flushing the tap before use significantly reduces copper in drinking water.
What causes high copper levels in Idaho tap water?
Copper typically leaches from copper pipes and brass fittings within homes, not from the water source itself. Corrosive (low pH or soft) water accelerates this leaching. Water utilities with high copper readings are required to adjust water chemistry to reduce corrosivity. You can reduce exposure by flushing your tap for 30 seconds before use.