Wastewater treatment plants in Idaho
94 facilities · 108 MGD combined flow
Klarifi tracks 94 publicly owned wastewater treatment plants in Idaho with a combined average flow of 108 MGD, serving about 879,926 residents. 16 plants treat more than 1 MGD and 2 more than 10 MGD; 64 use lagoon systems and 7 have digesters or biogas infrastructure. The largest is West Boise WWTP in Garden City at 50.91 MGD. 6 NPDES permits expire this year and 4 next year.
Every plant below links to a profile with average and design flow, the NPDES permit and its expiry, a three-year compliance snapshot and the capital projects planned in its city. Treatment technology and verified contacts are shown with a free Klarifi account.
94 plant locations in Idaho; dot size follows average flow.
NPDES permits and renewals in Idaho
Every plant discharges under an NPDES permit that is renewed every five years, usually with tighter limits. The renewal year is the year a plant budgets for upgrades.
Largest wastewater treatment plants in Idaho
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| West Boise WWTP | Garden City | 50.91 | 24 | ID0023981 | Jun 2027 | 10 |
| Nampa WWTP | Nampa | 10.69 | 11.76 | ID0022063 | Oct 2021 | 27 |
| Pocatello City WWTP | Pocatello | 6.38 | 12 | ID0021784 | Aug 2017 | 8 |
| Lewiston WWTP | Lewiston | 3.36 | 5.7 | ID0022055 | Jan 2021 | 0 |
| Jerome WWTP | Jerome | 3.33 | 3 | ID0020168 | Jun 2015 | 4 |
| Rexburg WWTP | Rexburg | 3.22 | 6 | ID0023817 | Mar 2028 | 41 |
| St Maries WWTP | Saint Maries | 2.25 | 2 | ID0022799 | Oct 2025 | 36 |
| Page WWTP | Smelterville | 2.04 | 4.3 | ID0021300 | Sep 2018 | 1 |
| Moscow STP | Moscow | 1.84 | 4 | ID0021491 | Jan 2031 | 0 |
| Oxbow WWTP | Shelley | 1.82 | 2 | ID0020133 | May 2019 | 0 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Idaho plants by treatment technology
All 94 plants in Idaho
Wastewater treatment in Idaho: questions
Sources and methodology
Flow, permit and violation figures come from the EPA's ICIS-NPDES discharge monitoring records. Population served comes from the Clean Watersheds Needs Survey 2022. Treatment structures are identified by Klarifi's review of aerial imagery, and capital improvement projects are extracted from published municipal budget documents. Violations are counted over the last three years of monitoring reports.
Data refreshed October 12, 2026.
Wastewater terms: WWTP · POTW · MGD · NPDES permit · Activated sludge · Oxidation ditch · all terms
Cite this page
Journalists, researchers and educators are welcome to quote these figures. Please credit Klarifi as the source and link to this page.
Klarifi. “Wastewater treatment plants in Idaho.” Updated October 12, 2026. https://klarifi.io/facilities/idahoNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.