Idaho Water Report Card: Worst Water Systems
The most contaminated public water systems in Idaho, ranked by PFAS levels, lead, and EPA violations from official EPA data.
Quick Answer
Capitol Water Corp has the highest PFAS in Idaho at 51 ppt (13x the EPA limit). Caldwell Housing Authority has the highest lead at 44 ppb. The tables below rank the worst systems in each category so you can see how your water compares.
Highest PFAS Levels in Idaho
Public water systems in Idaho with the highest peak PFAS ("forever chemical") reading in EPA UCMR5 testing (2023-2025). The EPA enforceable limit for PFOA and PFOS is 4 ppt.
| # | Water System | Location | Peak PFAS (ppt) | Compounds | vs 4 ppt limit |
|---|---|---|---|---|---|
| 1 | Capitol Water Corp | Boise · 9,000 served | 51 | 6 | 13x |
| 2 | Garden City Water And Sewer System | Garden City · 12,500 served | 28.2 | 7 | 7x |
| 3 | Mountain Home Air Force Base | Mountain Home Afb · 7,500 served | 13 | 4 | 3x |
| 4 | Rathdrum City Of | Rathdrum · 10,358 served | 8 | 2 | 2x |
| 5 | Lewiston City Of | Lewiston · 15,001 served | 5.6 | 3 | 1x |
| 6 | Meridian Water Dept | Meridian · 147,340 served | 4.9 | 1 | 1x |
| 7 | Payette City Of | Payette · 8,127 served | 4.3 | 1 | 1x |
Highest Lead Levels in Idaho
Community water systems in Idaho with the highest 90th-percentile lead result under the EPA Lead and Copper Rule. The EPA action level is 15 ppb; there is no safe level of lead for children.
| # | Water System | Location | Lead 90th-pctile (ppb) | vs 15 ppb |
|---|---|---|---|---|
| 1 | Caldwell Housing Authority | Caldwell · 1,100 served | 44 | 2.9x over |
| 2 | Fairview Water Dist | Preston · 1,300 served | 38 | 2.5x over |
| 3 | Mccall City Of | Mccall · 4,423 served | 34 | 2.3x over |
| 4 | Rathdrum City Of | Rathdrum · 10,358 served | 30 | 2.0x over |
| 5 | Bonners Ferry City Of | Bonners Ferry · 3,367 served | 27 | 1.8x over |
| 6 | Kamiah City Of | Kamiah · 1,495 served | 24 | 1.6x over |
| 7 | Orofino City Of | Orofino · 2,459 served | 14 | within |
| 8 | Three Mile Water Dist | Bonners Ferry · 2,458 served | 11 | within |
| 9 | Paul City Of | Paul · 1,195 served | 11 | within |
| 10 | Wilder City Of | Wilder · 1,690 served | 11 | within |
| 11 | Black Rock Utilities Inc | Hayden · 1,014 served | 10 | within |
| 12 | Rigby City Of | Rigby · 5,400 served | 10 | within |
Most EPA Violations in Idaho
Community water systems in Idaho with the most health-based EPA Safe Drinking Water Act violations on record. A health-based violation means a contaminant exceeded its federal limit or required treatment was not applied.
| # | Water System | Location | Health-based violations |
|---|---|---|---|
| 1 | Filer Water Works | Filer · 2,858 served | 22 |
| 2 | Ashton City Of | Ashton · 1,129 served | 16 |
| 3 | Salmon City Of | Salmon · 3,158 served | 14 |
| 4 | Mountain Home Air Force Base | Mountain Home Afb · 7,500 served | 14 |
| 5 | Mccall City Of | Mccall · 4,423 served | 11 |
| 6 | Fruitland City Of | Fruitland · 7,135 served | 5 |
| 7 | Capitol Water Corp | Boise · 9,000 served | 4 |
| 8 | Mountain Home, City Of | Mountain Home · 14,651 served | 3 |
| 9 | Bellevue City Of | Bellevue · 2,747 served | 2 |
| 10 | Blackfoot City Of | Blackfoot · 13,224 served | 2 |
| 11 | Franklin City Of | Franklin · 1,000 served | 2 |
| 12 | Preston City Of | Preston · 5,591 served | 2 |
How This Report Card Is Built
PFAS rankings use EPA UCMR5 monitoring (2023-2025), showing each system's peak detection above the 4 ppt EPA limit. Lead rankings use the EPA Lead and Copper Rule 90th-percentile tap results. Violation counts come from the EPA Safe Drinking Water Information System (SDWIS) and count health-based violations. Lead and violation lists are limited to community water systems serving 1,000 or more people. Figures are the most severe on record and do not necessarily reflect current treated water.
Frequently Asked Questions
What is the most PFAS-contaminated water system in Idaho?
In EPA UCMR5 testing (2023-2025), Capitol Water Corp in Boise had the highest recorded PFAS level in Idaho at 51 ppt - about 13x the EPA's 4 ppt limit for PFOA and PFOS.
Which Idaho water system has the highest lead levels?
Caldwell Housing Authority in Caldwell had the highest 90th-percentile lead result in Idaho under the EPA Lead and Copper Rule at 44 ppb - 2.9x the 15 ppb action level.
Which Idaho water system has the most EPA violations?
Filer Water Works in Filer has the most health-based EPA Safe Drinking Water Act violations on record in Idaho, with 22 violations.
Where does the Idaho water report card data come from?
PFAS figures come from EPA UCMR5 monitoring (2023-2025), lead from the EPA Lead and Copper Rule 90th-percentile tap results, and violations from EPA SDWIS health-based violation records. Figures are the most severe on record and do not necessarily reflect current treated water. Check your exact address at knowyourexposure.com.
What Idaho Residents Should Do
- Look up your exact address at knowyourexposure.com for your system's data
- See the full Idaho water quality overview
- If your system is listed, a certified filter (reverse osmosis for PFAS, NSF-53 for lead) reduces exposure at the tap. See the best water filters.