The biggest US wastewater operators are concentrated in major metropolitan areas, but the structure of the wastewater sector varies wildly by region. New York City’s Department of Environmental Protection (NYCDEP) runs 17 plants serving over 8 million people. The Puerto Rico Aqueduct and Sewer Authority (PRASA) operates a remarkable 49 plants — more than any other entity in the dataset — but serves only 1.8 million people, because Puerto Rico’s wastewater infrastructure is a patchwork of small dispersed facilities. This page ranks the country’s 50 biggest operators by population served and the 15 with the most plants, drawing on the EPA’s National Sewersheds dataset.
The map plots every one of the 17,272 publicly owned wastewater treatment plants in the US. Use the search box to find any operator’s plants by typing the operator name (e.g. “NYCDEP”, “Hampton Roads Sanitation”). For state-by-state breakdowns, see the main US wastewater treatment plants map.
Top 50 wastewater operators by population served
Population is the sum of residential populations served by all of the operator’s plants in the EPA’s 2022 Clean Watersheds Needs Survey. Operator names follow EPA spelling conventions; some longer official names have been shortened for readability.
| # | Operator | Plants | Population served |
|---|---|---|---|
| 1 | NYC Department of Environmental Protection (NYCDEP) | 17 | 8,059,570 |
| 2 | LA County Sanitation Districts | 11 | 6,136,504 |
| 3 | MWRD of Greater Chicago | 7 | 4,941,136 |
| 4 | Great Lakes Water Authority (Detroit) | 1 | 2,844,020 |
| 5 | Miami-Dade Water & Sewer Department | 3 | 2,831,094 |
| 6 | LA City Bureau of Sanitation | 1 | 2,800,773 |
| 7 | San Diego Metropolitan Wastewater Department | 3 | 2,753,498 |
| 8 | King County (Seattle metro) | 5 | 2,597,671 |
| 9 | Met Council Environmental Services (Twin Cities) | 3 | 2,465,234 |
| 10 | Massachusetts Water Resources Authority | 2 | 2,334,296 |
| 11 | Orange County Sanitation District (CA) | 2 | 2,044,881 |
| 12 | DC Water (Blue Plains) | 1 | 2,016,161 |
| 13 | Metro Wastewater Reclamation District (Denver) | 1 | 1,964,761 |
| 14 | City of Phoenix | 2 | 1,844,039 |
| 15 | PRASA (Puerto Rico Aqueduct & Sewer Authority) | 49 | 1,816,727 |
| 16 | Sacramento Regional CSD | 1 | 1,771,809 |
| 17 | Allegheny County Sanitary Authority | 1 | 1,720,786 |
| 18 | City of Houston | 39 | 1,639,330 |
| 19 | Hampton Roads Sanitation District (VA) | 15 | 1,630,899 |
| 20 | Trinity River Authority of Texas | 5 | 1,531,301 |
| 21 | Passaic Valley Sewerage Commission | 1 | 1,477,833 |
| 22 | City of Austin | 5 | 1,431,741 |
| 23 | City of San Jose Environmental Services | 1 | 1,389,338 |
| 24 | San Antonio Water System | 3 | 1,376,784 |
| 25 | Columbus Division of Sewerage and Drainage | 2 | 1,350,231 |
| 26 | Charlotte Water | 5 | 772,883 |
| 27 | Des Moines Wastewater Reclamation Authority | 1 | 748,123 |
| 28 | City of Portland (OR) | 4 | 744,225 |
| 29 | City of Memphis | 2 | 725,464 |
| 30 | Orange County Utilities (FL) | 4 | 712,456 |
| 31 | Gwinnett County DWR | 3 | 710,000 |
| 32 | Ocean County Utilities Authority | 3 | 705,431 |
| 33 | City of Las Vegas | 2 | 683,166 |
| 34 | Oklahoma City Water Utilities Trust | 4 | 680,653 |
| 35 | Clean Water Services (Oregon) | 3 | 667,392 |
| 36 | City of Raleigh | 3 | 607,312 |
| 37 | Monroe County (NY) | 2 | 593,666 |
| 38 | Bergen County Utilities Authority | 2 | 589,527 |
| 39 | San Francisco Public Utilities Commission | 1 | 585,360 |
| 40 | Baltimore Department of Public Works | 1 | 573,186 |
| 41 | Westchester County Department of Environmental Facilities | 4 | 571,456 |
| 42 | Louisville & Jefferson County MSD | 1 | 569,690 |
| 43 | Albuquerque Bernalillo Water Utility Authority | 1 | 564,559 |
| 44 | Northeast Ohio Regional Sewer District | 1 | 555,185 |
| 45 | Central Contra Costa Sanitary District | 1 | 552,952 |
| 46 | Philadelphia Water Department | 1 | 547,807 |
| 47 | City of Wilmington (DE) | 1 | 530,079 |
| 48 | Central Valley WRF Board (Salt Lake City) | 1 | 528,146 |
| 49 | Kansas City Water Services Department | 1 | 525,071 |
| 50 | Jefferson County Commission | 14 | 524,387 |
The 15 operators with the most plants
Plant count is a different measure than population served — it reflects the geographic structure of the operator’s territory rather than the size of the population it covers. The list below is dominated by regional sewer districts in territories with widely scattered communities (Puerto Rico, the Texas Gulf Coast, suburban Long Island) and one outlier: a consulting engineering firm that operates 16 small plants on contract.
| # | Operator | Plants | Population served |
|---|---|---|---|
| 1 | PRASA (Puerto Rico) | 49 | 1,816,727 |
| 2 | City of Houston | 39 | 1,639,330 |
| 3 | Jefferson County Public Sewer District (MO) | 25 | 15,695 |
| 4 | CGCRCSD | 20 | 10,010 |
| 5 | Suffolk County Department of Public Works (NY) | 20 | 171,259 |
| 6 | Boone County Regional Sewer District (MO) | 18 | 20,146 |
| 7 | NYC Department of Environmental Protection | 17 | 8,059,570 |
| 8 | GMS, Inc. Consulting Engineers (contract operator) | 16 | 13,713 |
| 9 | Hampton Roads Sanitation District (VA) | 15 | 1,630,899 |
| 10 | Jefferson County Commission | 14 | 524,387 |
| 11 | Berkeley County PSSD | 12 | 30,928 |
| 12 | Louisville & Jefferson County MSD | 12 | 16,910 |
| 13 | Geauga County Department of Water Resources (OH) | 11 | 6,711 |
| 14 | LA County Sanitation Districts | 11 | 6,136,504 |
| 15 | Board of Selectmen | 10 | 24,005 |
Three structural patterns in US wastewater operations
Mega-operator, mega-population
NYCDEP, LA County Sanitation Districts, and MWRD of Greater Chicago are the canonical mega-operators — large public agencies running multiple very large plants serving consolidated metropolitan populations. They top both the population and plant-count rankings simultaneously. These operators tend to have integrated sewer collection systems, advanced treatment plants, and biosolids programmes that are themselves substantial public works.
Single-mega-plant operators
A surprising number of major US cities are served by a single dominant treatment plant operated by a single agency: Detroit (GLWA, one plant for 2.84 million), Boston (MWRA Deer Island), Pittsburgh (ALCOSAN), Sacramento, Denver, Newark (Passaic Valley), San Jose, San Francisco, Albuquerque, Cleveland (NEORSD), and Philadelphia all run their entire wastewater stream through a single mega-plant. This concentration is efficient and economical — a single plant typically captures economies of scale unavailable to smaller systems — but it also creates concentrated risk: a disruption at any of these plants can affect millions of people overnight.
Many-small-plants operators
At the other end of the spectrum are operators that run many small plants serving widely scattered communities. PRASA’s 49 plants in Puerto Rico average 37,000 people each. The City of Houston’s 39 plants average just 42,000 people each, reflecting the city’s enormous geographic footprint. Hampton Roads Sanitation District’s 15 plants average 109,000 people each but cover the seven cities of the Hampton Roads region. Many-small-plants operators face the opposite challenge of mega-operators: high per-capita operating costs and the difficulty of upgrading dozens of plants simultaneously to meet new effluent standards.
The largest single-plant operators
If you filter the data to operators that run only one plant, the rankings change dramatically. Of the top 50 by population, 19 are single-plant operators — mostly large cities that have consolidated all their wastewater into one regional facility. The largest single-plant operator in the US is the Great Lakes Water Authority (Detroit), with one plant serving 2.84 million people. Other notable single-plant giants include DC Water (Blue Plains), the Allegheny County Sanitary Authority (ALCOSAN, Pittsburgh), the Sacramento Regional County Sanitation District, and the Metro Wastewater Reclamation District (Denver).
Why the operator matters
The operator behind a wastewater treatment plant determines who is responsible when something goes wrong, who issues sewer bills, who plans for capacity expansion, and who is on the hook for upgrades to meet PFAS, nutrient, or biosolids regulations. For the contamination angle, see our PFAS contamination map; for industrial-water inputs to municipal sewers, see the map of EPA-permitted industrial stormwater facilities; and for the drinking-water side of the same cycle, see our interactive map of US tap water quality. Plant-by-plant compliance and enforcement history is at echo.epa.gov — the link in each plant card on the embedded map will take you straight to the relevant facility.
Frequently asked questions
Why does PRASA appear with 49 plants but a relatively small population?
PRASA — the Puerto Rico Aqueduct and Sewer Authority — is the sole wastewater operator across the entire territory of Puerto Rico. It runs many small plants serving individual towns and rural communities, rather than a few large plants serving consolidated metro populations. The total population on Puerto Rico’s central sewer system is about 1.8 million, well below the 3.3 million population of the territory, with the remainder on private septic systems.
Why are there so many “Jefferson County” entries?
The US has Jefferson Counties in 26 states, several of which run their own sewer agencies. Three appear in the top 100 by plant count: Jefferson County Public Sewer District (Missouri, 25 plants), Louisville & Jefferson County MSD (Kentucky, 12 plants — the entry in the operator list with the Morris Forman WQTC), and Jefferson County Commission (Alabama, 14 plants).
Are private contract operators included?
Only when they are the listed operator of record for a publicly owned plant. GMS, Inc. Consulting Engineers appears in the top 15 by plant count because they are the contract operator for 16 small public plants. Private wastewater treatment plants serving industrial sites are not included — this dataset is restricted to publicly owned treatment works (POTWs) under the Clean Water Act.
