| METROPOLITAN DISTRICT COMMISSION | 390,887 | 3 | Clean |
| CTWC - NORTHERN REG-WESTERN SYSTEM | 101,313 | 406 | Detected |
| NEW BRITAIN WATER DEPARTMENT | 73,534 | 34 | Clean |
| BRISTOL WATER DEPARTMENT | 52,079 | 269 | Detected |
| MANCHESTER WATER DEPARTMENT | 51,198 | 31 | Detected |
| SOUTHINGTON WATER DEPARTMENT | 43,069 | 1,028 | Detected |
| HAZARDVILLE WATER COMPANY | 18,544 | 119 | Detected |
| AQUARION-PLAINVILLE REGIONAL | 18,231 | 63 | Detected |
| CTWC - UNIONVILLE SYSTEM | 14,693 | 27 | Detected |
| AQUARION-SIMSBURY REGIONAL | 14,691 | 200 | Detected |
| AVON WATER CO | 11,590 | 476 | Detected |
| KENSINGTON FIRE DISTRICT | 7,553 | 96 | Clean |
| CTWC - NAUGATUCK REG-COLLINSVILLE SYS | 6,324 | 66 | Detected |
| BERLIN WATER CONTROL COMMISSION | 5,128 | 677 | Detected |
| WORTHINGTON FIRE DISTRICT | 2,875 | 57 | — |
| CONNECTICUT CORRECTIONAL INSTITUTE | 2,385 | 460 | — |
| SALMON BROOK DISTRICT WATER DEPT | 2,151 | 127 | — |
| TARIFFVILLE FIRE DISTRICT WATER DEPT | 1,477 | 112 | — |
| AQUARION-MARLBOROUGH | 1,348 | 633 | — |
| TALCOTT MOUNTAIN S.P. | 793 | 22 | — |
| LAKE GARDA SCHOOL | 715 | 27 | — |
| PENWOOD STATE PARK/MAIN PARK WELL | 700 | 13 | — |
| CHERRY BROOK SCHOOL | 615 | 260 | — |
| AQUARION-SUFFIELD | 595 | 121 | — |
| ELISABETH M. BENNET ACADEMY | 536 | 72 | — |
| EASTBURY SCHOOL | 523 | 98 | — |
| CTWC - REDWOOD FARMS DIVISION | 424 | 24 | — |
| WELLS ROAD INTERMEDIATE SCHOOL | 405 | 126 | — |
| THE MASTERS SCHOOL | 372 | 173 | — |
| AQUARION-NORTH MOUNTAIN | 370 | 4 | — |
| TURKEY HILL OF EAST GRANBY, LLC | 360 | 153 | — |
| GQC WELL COMMISSION | 360 | 340 | — |
| KELLY LANE PRIMARY SCHOOL | 357 | 21 | — |
| NEWINGTON VA MEDICAL CENTER-BUILDING 2E | 335 | 6 | — |
| ETHEL WALKER SCHOOL | 325 | 567 | — |
| HARTLAND ELEM SCH & TOWN BLDGS | 300 | 392 | — |
| APPLE REHAB | 238 | 12 | — |
| CTWC - CHIMNEY HILL | 227 | 2 | — |
| MANCHESTER CONG. OF JEHOVAHS WITNESSES | 222 | 8 | — |
| CANNABIS RETAILER AT 195 ALBANY TURNPIKE | 214 | 7 | — |
| OLD NEWGATE RIDGE WATER COMPANY INC | 208 | 166 | — |
| WINDING TRAILS RECREATION ASSN - UPPER | 207 | 17 | — |
| WINDING TRAILS RECREATION ASSN - LOWER | 207 | 4 | — |
| SHAKER HEIGHTS WATER COMPANY | 172 | 41 | — |
| CTWC - SACHEM VILLAGE CONDO | 166 | 9 | — |
| MARLBOROUGH HEALTH CARE CENTER, INC | 165 | 142 | — |
| CHELSEA COMMON CONDOMINIUM ASSOCIATION | 126 | 27 | — |
| CCARC INC. | 125 | 19 | — |
| CADENCE ACADEMY | 112 | 738 | — |
| CTWC - MARLBOROUGH GARDENS | 110 | 38 | — |