Klarifi tracks 678 publicly owned wastewater treatment plants in Iowa with a combined average flow of 2 MGD, serving about 1,530,298 residents. 0 plants treat more than 1 MGD and 0 more than 10 MGD; 631 use lagoon systems and 69 have digesters or biogas infrastructure. The largest is Walnut City Of STP in Walnut at 0.99 MGD. 71 NPDES permits expire this year and 95 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. Showing facilities 1–200 of 678 by average flow — browse the rest with the page links below.
678 plant locations in Iowa; dot size follows average flow.
NPDES permits and renewals in Iowa
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.
The 10 largest publicly owned wastewater treatment plants in Iowa by average flow, with NPDES permit, expiry and three-year violation count. Source: EPA ICIS-NPDES via Klarifi.
Klarifi tracks 678 publicly owned wastewater treatment plants in Iowa with a combined average flow of 2 million gallons per day, serving about 1,530,298 residents. 0 of them treat more than 1 MGD and 0 more than 10 MGD.
Walnut City Of STP in Walnut is the largest plant in Iowa by average flow, treating about 0.99 MGD.
631 of Iowa's plants use lagoon systems and 69 have biogas or anaerobic digestion infrastructure, based on Klarifi's aerial imagery review.
71 permits held by Iowa plants expire in 2026 and 95 in 2027. Renewals typically bring new limits and trigger upgrade projects.
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 September 14, 2026.
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