| MIDDLETOWN WATER DEPARTMENT | 41,019 | 26 | Clean |
| CROMWELL FIRE DISTRICT WATER DEPARTMENT | 14,316 | 232 | Detected |
| CTWC - SHORELINE REGION-CHESTER SYSTEM | 5,030 | 156 | Clean |
| PORTLAND WATER DEPARTMENT | 5,010 | 65 | Detected |
| CONNECTICUT VALLEY HOSPITAL | 2,928 | 149 | — |
| PRATT & WHITNEY | 2,800 | 187 | — |
| DURHAM CENTER DIVISION | 1,601 | 298 | — |
| HADDAM KILLINGWORTH INTER/MIDDLE SCHOOL | 808 | 308 | — |
| HADDAM MEADOWS S.P. | 780 | 50 | — |
| CTWC - JENSENS BEECHWOOD SYSTEM | 750 | 447 | — |
| CTWC - SPICE HILL DIVISION | 712 | 210 | — |
| YMCA CAMP INGERSOLL | 653 | 5 | — |
| CTWC - LAKE HAYWARD | 650 | 86 | — |
| HADDAM-KILLINGWORTH HIGH SCHOOL | 642 | 85 | — |
| NATHAN HALE-RAY MIDDLE SCHOOL | 620 | 7 | — |
| EAST HADDAM ELEMENTARY SCHOOL | 600 | 17 | — |
| EAST HAMPTON HIGH SCHOOL | 568 | 332 | — |
| VALLEY REGIONAL HIGH SCHOOL | 565 | 23 | — |
| EDGEMERE CONDOMINIUM ASSN., INC. | 540 | 297 | — |
| WADSWORTH FALLS/BATHROOM WELL | 527 | 13 | — |
| YESHIVA OF WATERBURY-DURHAM CAMPUS | 490 | 1,081 | — |
| EAST HAMPTON MIDDLE SCHOOL | 487 | 118 | — |
| NATHAN HALE-RAY HIGH SCHOOL | 461 | 4 | — |
| WHELEN ENGINEERING CO | 400 | 33 | — |
| JOHN WINTHROP JUNIOR HIGH SCHOOL | 400 | 20 | — |
| FREDERICK BREWSTER SCHOOL | 370 | 33 | — |
| EAST HAMPTON WPCA - VILLAGE CENTER | 366 | 264 | — |
| BURR DISTRICT ELEMENTARY SCHOOL | 364 | 381 | — |
| EAST HAMPTON WPCA - ROYAL OAKS SYSTEM | 328 | 303 | — |
| KILLINGWORTH ELEMENTARY SCHOOL | 315 | 21 | — |
| DEER LAKE OUTDOOR CENTER DINING - WELL 2 | 300 | 10 | — |
| JOHN LYMAN SCHOOL | 285 | 19 | — |
| CTWC - BANNER VILLAGE | 265 | 43 | — |
| CTWC - SHORELINE REG-CHESTER VLLG WEST | 216 | 94 | — |
| HERITAGE COVE CONDOMINIUMS | 208 | 93 | — |
| CTWC - BAKER HILL DIVISION | 203 | 201 | — |
| HOBSON MOTZER, INC. | 200 | 239 | — |
| 732 MIDDLESEX TURNPIKE | 200 | 20 | — |
| THE INDEPENDENT DAY SCHOOL | 199 | 6 | — |
| AQUARION-EAST HAMPTON | 189 | 5 | — |
| ST. CLEMENTS MARINA | 180 | 0 | — |
| MALLARD COVE CONDOMINIUM ASSN. | 177 | 262 | — |
| DD DURHAM | 156 | 10 | — |
| EAST HADDAM MUNICIPAL CENTER | 154 | 512 | — |
| CTWC - WESTCHESTER EAST | 153 | 349 | — |
| GOODSPEED OPERA HOUSE | 150 | 332 | — |
| CLINTON NURSERIES - SECONDARY SYSTEM | 143 | 11 | — |
| COBALT LODGE HEALTHCARE & REHAB CENTER | 130 | 204 | — |
| CHESTELM HEALTH & REHABILITATION CENTER | 120 | 47 | — |
| EVERGREEN SPRINGS - SYSTEM #4 | 110 | 356 | — |