The 50 largest wastewater treatment plants in Maryland
Ranked by average flow · 277 MGD combined · 99% of the state's reported flow
Back River Wastewater Treatment Plant in Baltimore is the largest publicly owned wastewater treatment plant in Maryland by reported average flow, treating about 107.68 million gallons per day. The 50 plants below treat 277 MGD between them, 99% of the flow reported by all 117 plants in the state, and serve about 1,743,433 people. Every plant links to its profile with permit and compliance data. Treatment technology is shown with a free Klarifi account.
| # | Facility | City | Avg flow (MGD) | Population | NPDES permit | Expires | Violations (3y) |
|---|---|---|---|---|---|---|---|
| 1 | Back River Wastewater Treatment Plant | Baltimore | 107.68 | 432,114 | MDL021555 | Dec 2030 | 32 |
| 2 | Patapsco Wastewater Treatment Plant | Baltimore | 51.59 | 293,367 | MDL021601 | Dec 2030 | 22 |
| 3 | Piscataway Swge Plnt | Accokeek | 19.8 | 160,827 | MDL021539 | Dec 2030 | 25 |
| 4 | Little Patuxent Water Reclamation Plant | Savage | 16.76 | 125,350 | MD0055174 | May 2031 | 8 |
| 5 | Sod Run Wastewater Treatment Plant | Perryman | 9.48 | 122,618 | MDL056545 | Dec 2030 | 0 |
| 6 | Annapolis WRF | Annapolis | 7.94 | 47,859 | MD0021814 | Jan 2030 | 6 |
| 7 | Ballenger-Mckinney WWTP | Frederick | 7.11 | 69,525 | MD0021822 | Dec 2030 | 1 |
| 8 | Parkway Wastewater Treatment Plant | Laurel | 6.09 | 56,093 | MDL021725 | Dec 2030 | 2 |
| 9 | City Of Frederick Wastewater Treatment Plant-2012 | Frederick | 5.68 | 72,481 | MD0021610 | May 2031 | 23 |
| 10 | The City Of Bowie (ssos) | Bowie | 5.09 | 25,000 | MDL021628 | Dec 2030 | 7 |
| 11 | City Of Salisbury Wastewater Treatment Plant | Salisbury | 4.71 | 24,205 | MDL021571 | Dec 2030 | 83 |
| 12 | Ocean City Wastewater Treatment Plant | Ocean City | 4.45 | 12,500 | MDL020044 | Dec 2030 | 2 |
| 13 | Broadneck Water Reclamation Facility | Annapolis | 3.79 | — | MDL021644 | Dec 2030 | 100 |
| 14 | Westminster WWTP | Westminster | 3.6 | 38,000 | MD0021831 | Jul 2031 | 9 |
| 15 | Conococheague WWTP | Williamsport | 2.26 | 12,180 | MD0063509 | May 2031 | 0 |
| 16 | Easton WWTP | Easton | 2.19 | 16,143 | MDL020273 | Dec 2030 | 2 |
| 17 | Freedom District WWTP | Sykesville | 1.97 | 24,913 | MD0021512 | Oct 2029 | 32 |
| 18 | Maryland City Water Reclamation Facility | Laurel | 1.49 | 20,309 | MDL062596 | Dec 2030 | 21 |
| 19 | Northeast River Advanced WWTP | Charlestown | 1.35 | 27,330 | MDL052027 | Dec 2030 | 32 |
| 20 | Celanese WWTP | Cumberland | 1.11 | 2,122 | MDL063878 | Dec 2030 | 0 |
| 21 | Town Of La Plata | La Plata | 1.08 | 21,326 | MDL020524 | Dec 2030 | 90 |
| 22 | George'S Creek WWTP | Westernport | 1.03 | 6,035 | MD0060071 | May 2026 | 0 |
| 23 | Wssc Damascus WRRF | Gaithersburg | 0.76 | 5,246 | MD0020982 | Dec 2028 | 3 |
| 24 | Taneytown Wastewater Treatment Plant | Taneytown | 0.75 | 6,746 | MD0020672 | May 2031 | 3 |
| 25 | Mount Airy WWTP | Mount Airy | 0.63 | 9,701 | MD0022527 | Dec 2025 | 143 |
| 26 | Delmar WWTP | Delmar | 0.62 | 7,624 | MD0020532 | Jul 2031 | 6 |
| 27 | Chestertown WWTP | Chestertown | 0.6 | 6,200 | MD0020010 | Sep 2026 | 5 |
| 28 | Pocomoke City Wastewater Treatment Facility | Pocomoke City | 0.53 | 4,905 | MD0022551 | May 2028 | 46 |
| 29 | Hampstead WWTP | Hampstead | 0.49 | 4,207 | MD0022446 | Aug 2030 | 25 |
| 30 | Piney Orchard WWTP | Odenton | 0.47 | 8,500 | MDL059145 | Dec 2030 | 6 |
| 31 | Fruitland WWTP | Fruitland | 0.46 | 4,127 | MD0052990 | Feb 2029 | 36 |
| 32 | Poolesville WWTP | Poolesville | 0.43 | 5,500 | MD0023001 | Nov 2027 | 6 |
| 33 | Manchester WWTP | Manchester | 0.42 | 5,118 | MD0022578 | Feb 2027 | 72 |
| 34 | Trout Run WWTP | Mountain Lake Park | 0.42 | 12,612 | MD0051497 | Sep 2016 | 3 |
| 35 | Centreville WWTP | Centreville | 0.42 | 4,569 | MD0020834 | Nov 2026 | 12 |
| 36 | Denton WWTP | Denton | 0.39 | 5,490 | MD0020494 | Jul 2025 | 0 |
| 37 | Town Of Emmitsburg | Emmitsburg | 0.35 | 2,900 | MD0020257 | Feb 2030 | 13 |
| 38 | Indian Head WWTP | Indian Head | 0.31 | 3,625 | MD0020052 | Feb 2030 | 1 |
| 39 | St. Michael'S WWTP | Saint Michaels | 0.3 | 4,445 | MD0023604 | Nov 2030 | 0 |
| 40 | Worton-Butlertown WWTP | Worton | 0.29 | 1,160 | MD0060585 | Oct 2029 | 5 |
| 41 | Boonsboro WWTP | Boonsboro | 0.28 | 7,998 | MD0020231 | Dec 2030 | 1 |
| 42 | Oakland WWTP | Oakland | 0.28 | 2,058 | MD0020648 | Mar 2024 | 1 |
| 43 | Grantsville WWTP | Grantsville | 0.28 | 1,253 | MD0020761 | Jun 2031 | 147 |
| 44 | Snow Hill WWTP | Snow Hill | 0.25 | 2,879 | MD0022764 | Dec 2028 | 60 |
| 45 | Federalsburg WWTP | Federalsburg | 0.24 | 2,794 | MD0020249 | Jan 2029 | 391 |
| 46 | Hancock WWTP | Hancock | 0.23 | 4,100 | MD0024562 | May 2031 | 24 |
| 47 | Rising Sun Town Of WWTP | Rising Sun | 0.22 | 3,168 | MD0020265 | Apr 2028 | 22 |
| 48 | Smithsburg WWTP | Smithsburg | 0.22 | 3,250 | MD0024317 | Mar 2031 | 14 |
| 49 | Rock Hall WWTP | Rock Hall | 0.21 | 2,961 | MD0020303 | Jul 2029 | 7 |
| 50 | Pinto/md Water Services WWTP | Pinto | 0.21 | — | MD0022748 | May 2028 | 31 |
Treatment technology for each plant is shown with a free Klarifi account. Create one →
Largest plants in Maryland: 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 · Tertiary treatment · Significant industrial user · 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. “Largest wastewater treatment plants in Maryland (2026).” Updated October 26, 2026. https://klarifi.io/facilities/maryland/largestNeed a custom cut of the data for a state, a county or a list of plants? Email info@klarifi.io.