NPDES permit lookup

Search 12,584 publicly owned wastewater treatment plants by permit number or name. Every result opens the plant with its permit status, expiry date, design flow, treatment technology and three-year violation count.

Effective permits

9,203

Administratively continued

2,349

Expiring in 2026

1,194

Expiring in 2027

2,002

Why permit expiry dates matter

An NPDES permit runs for five years. To keep discharging, a plant must apply for renewal at least 180 days before the expiry date, and the renewed permit usually arrives with tighter effluent limits, new monitoring requirements or a compliance schedule. That is why the year a permit expires is the year a plant starts budgeting for upgrades: nutrient removal, disinfection, capacity or controls.

NPDES permit search by state

NPDES permit questions

What is an NPDES permit?

An NPDES (National Pollutant Discharge Elimination System) permit authorises a facility to discharge treated wastewater to surface water under the Clean Water Act. It sets effluent limits, monitoring and reporting requirements, and runs for at most five years before it must be renewed.

How do I read an NPDES permit number?

A permit number is two letters and seven characters, for example TX0021873. The letters are the state; the digits identify the permit. General permits carry a G (for example ILG580094). Type the number into the lookup above to open the plant that holds it.

How many NPDES permits are administratively continued?

Of the 12,584 publicly owned plants in the directory, 9,203 hold effective permits, 2,349 are administratively continued (renewal applied for, old permit still in force) and 964 are recorded as expired.

How many wastewater permits expire in 2026 and 2027?

1,194 permits held by publicly owned plants expire in 2026 and 2,002 in 2027. Each state has a renewal calendar listing the plants by expiry month.

Where do I find the official permit document?

The issuing state agency (or the EPA region in Massachusetts, New Hampshire and New Mexico) publishes the permit and fact sheet. Each state page below names the agency and links to it; the plant profile shows the permit number to search for.

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: NPDES permit · POTW · Significant industrial user · MGD · Anaerobic digester · Lift station · all terms

Try Klarifi for free

Create your own trial account and explore how Klarifi can help you.

Try for free