| CTWC - NAUGATUCK REG-TERRYVILLE SYSTEM | CLINTON, CT | 5,607 | 9 | Clean |
| BERLIN WATER CONTROL COMMISSION | BERLIN, CT | 5,128 | 677 | Detected |
| CTWC - SHORELINE REGION-CHESTER SYSTEM | CLINTON, CT | 5,030 | 156 | Clean |
| PORTLAND WATER DEPARTMENT | PORTLAND, CT | 5,010 | 65 | Detected |
| COLCHESTER SEWER & WATER COMMISSION | COLCHESTER, CT | 4,020 | 159 | Detected |
| CTWC - NAUGATUCK REG-THOMASTON SYSTEM | CLINTON, CT | 3,789 | 84 | Clean |
| LEDYARD WPCA - LEDYARD CENTER | LEDYARD, CT | 3,294 | 13 | — |
| AQUARION-LITCHFIELD REGIONAL | SHELTON, CT | 3,097 | 12 | Clean |
| CTWC - SHORELINE REGION-SOUND VIEW | CLINTON, CT | 3,028 | 134 | — |
| CONNECTICUT VALLEY HOSPITAL | MIDDLETOWN, CT | 2,928 | 149 | — |
| WORTHINGTON FIRE DISTRICT | BERLIN, CT | 2,875 | 57 | — |
| PRATT & WHITNEY | MIDDLETOWN, CT | 2,800 | 187 | — |
| FAIRFIELD HILLS | NEWTOWN, CT | 2,610 | 64 | — |
| WESTON SCHOOLS AND MUNICIPAL BUILDINGS | WESTON, CT | 2,600 | 493 | — |
| RIDGEFIELD HIGH AND MIDDLE SCHOOL | RIDGEFIELD, CT | 2,575 | 100 | — |
| SCWA, MONTVILLE DIVISION (MTV) | GALES FERRY, CT | 2,570 | 28 | — |
| SCWA, TOWER-FERRY VIEW DIVISION | GALES FERRY, CT | 2,567 | 54 | — |
| WOLCOTT WATER DEPARTMENT | WOLCOTT, CT | 2,550 | 137 | — |
| CTWC - GALLUP SYSTEM | CLINTON, CT | 2,538 | 46 | — |
| GROTON LONG POINT ASSOCIATION | GROTON, CT | 2,400 | 69 | — |
| CONNECTICUT CORRECTIONAL INSTITUTE | WETHERSFIELD, CT | 2,385 | 460 | — |
| LEDYARD WPCA, GALES FERRY SYSTEM | LEDYARD, CT | 2,369 | 23 | — |
| SALMON BROOK DISTRICT WATER DEPT | GRANBY, CT | 2,151 | 127 | — |
| NOANK FIRE DISTRICT | NOANK, CT | 1,947 | 59 | — |
| AQUARION-SALISBURY | SHELTON, CT | 1,932 | 23 | — |
| CTWC - HEBRON CENTER DIVISION | CLINTON, CT | 1,927 | 2 | — |
| AQUARION-NEW HARTFORD | SHELTON, CT | 1,872 | 132 | Clean |
| SCWA, NORTH STONINGTON DIVISION (NST) | GALES FERRY, CT | 1,860 | 33 | — |
| NEW FAIRFIELD HIGH/MIDDLE SCHOOL | NEW FAIRFIELD, CT | 1,791 | 576 | — |
| CTWC - PLAINFIELD SYSTEM | CLINTON, CT | 1,713 | 23 | — |
| DURHAM CENTER DIVISION | DURHAM, CT | 1,601 | 298 | — |
| AQUARION-NORTH CANAAN | SHELTON, CT | 1,481 | 15 | — |
| TARIFFVILLE FIRE DISTRICT WATER DEPT | TARIFFVILLE, CT | 1,477 | 112 | — |
| LEONARD J.TYL MIDDLE SCHOOL&HIGH SCHOOL | OAKDALE, CT | 1,466 | 328 | — |
| SCWA, MOHEGAN DIVISION | GALES FERRY, CT | 1,428 | 17 | — |
| CONSOLIDATED & MEETING HOUSE HILL SCHOOL | NEW FAIRFIELD, CT | 1,425 | 294 | — |
| KILLINGLY HIGH SCHOOL & AGRICULTURAL CTR | DAYVILLE, CT | 1,400 | 128 | — |
| CTWC - LEGEND HILL SYSTEM | CLINTON, CT | 1,368 | 118 | — |
| AQUARION-MARLBOROUGH | SHELTON, CT | 1,348 | 633 | — |
| CANDLEWOOD SHORES TAX DISTRICT | BETHEL, CT | 1,315 | 382 | — |
| MONTVILLE WATER SUPPLY | UNCASVILLE, CT | 1,300 | 87 | — |
| COVENTRY HIGH & NATHAN HALE SCHOOLS | COVENTRY, CT | 1,252 | 18 | — |
| TOLLAND WATER DEPARTMENT | TOLLAND, CT | 1,251 | 19 | — |
| LONE OAK CAMPGROUND | QUINCY, CT | 1,250 | 29 | — |
| AQUARION-WOODBURY | SHELTON, CT | 1,209 | 231 | — |
| WOODSTOCK ACADEMY | WOODSTOCK, CT | 1,125 | 199 | — |
| REGION 18 SCHOOLS - LYME STREET | OLD LYME, CT | 1,102 | 130 | — |
| AQUARION-EAST DERBY | SHELTON, CT | 1,101 | 32 | — |
| CTWC - THOMPSON SYSTEM | CLINTON, CT | 1,070 | 77 | — |
| CTWC - SHORELINE REGION-POINT O WOODS | CLINTON, CT | 1,068 | 113 | — |