Wastewater treatment plants in Hawaii
3 facilities · 4 MGD combined flow
Klarifi tracks 3 publicly owned wastewater treatment plants in Hawaii with a combined average flow of 4 MGD, serving about 46,001 residents. 1 plants treat more than 1 MGD and 0 more than 10 MGD; 0 use lagoon systems and 1 have digesters or biogas infrastructure. The largest is Hawaii County Hilo WWTP in Hilo at 3.85 MGD.
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.
3 plant locations in Hawaii; dot size follows average flow. Boundaries: U.S. Census Bureau.
NPDES permits and renewals in Hawaii
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 Hawaii
| Facility | City | Avg flow (MGD) | Design (MGD) | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|
| Hawaii County Hilo WWTP | Hilo | 3.85 | 5 | HI0021377 | Apr 2030 | 52 |
| Wailua Wastewater Treatment Plant | Kapaa | 0.48 | 1.5 | HI0020257 | Oct 2024 | 4 |
| County Of Hawaii Papaikou-Paukaa WWTP | Hilo | 0.1 | 0.35 | HI0021113 | Apr 2031 | 40 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
All 3 plants in Hawaii
| Facility | City | Flow (MGD) |
|---|---|---|
| Hawaii County Hilo WWTP | Hilo | 3.85 |
| Wailua Wastewater Treatment Plant | Kapaa | 0.48 |
| County Of Hawaii Papaikou-Paukaa WWTP | Hilo | 0.1 |
Wastewater treatment in Hawaii: 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 26, 2026.
Wastewater terms: WWTP · POTW · MGD · NPDES permit · Equalization tank · Centrate · 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 Hawaii.” Updated October 26, 2026. https://klarifi.io/facilities/hawaiiNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.