| NORWICH PUBLIC UTILITIES | 36,163 | 97 | Detected |
| GROTON UTILITIES | 30,200 | 6 | Clean |
| NEW LONDON DEPT. OF PUBLIC UTILITIES | 27,620 | 203 | Clean |
| WATERFORD WPCA | 16,578 | 104 | Clean |
| EAST LYME WATER & SEWER COMMISSION | 15,245 | 532 | Detected |
| AQUARION-MYSTIC | 10,788 | 162 | Detected |
| JEWETT CITY WATER COMPANY | 6,840 | 134 | Detected |
| COLCHESTER SEWER & WATER COMMISSION | 4,020 | 159 | Detected |
| LEDYARD WPCA - LEDYARD CENTER | 3,294 | 13 | — |
| CTWC - SHORELINE REGION-SOUND VIEW | 3,028 | 134 | — |
| SCWA, MONTVILLE DIVISION (MTV) | 2,570 | 28 | — |
| SCWA, TOWER-FERRY VIEW DIVISION | 2,567 | 54 | — |
| GROTON LONG POINT ASSOCIATION | 2,400 | 69 | — |
| LEDYARD WPCA, GALES FERRY SYSTEM | 2,369 | 23 | — |
| NOANK FIRE DISTRICT | 1,947 | 59 | — |
| SCWA, NORTH STONINGTON DIVISION (NST) | 1,860 | 33 | — |
| LEONARD J.TYL MIDDLE SCHOOL&HIGH SCHOOL | 1,466 | 328 | — |
| SCWA, MOHEGAN DIVISION | 1,428 | 17 | — |
| MONTVILLE WATER SUPPLY | 1,300 | 87 | — |
| REGION 18 SCHOOLS - LYME STREET | 1,102 | 130 | — |
| CTWC - SHORELINE REGION-POINT O WOODS | 1,068 | 113 | — |
| SPRAGUE WATER & SEWER AUTHORITY | 1,058 | 192 | — |
| STRAWBERRY PARK | 1,047 | 65 | — |
| ST. BERNARD SCHOOL | 950 | 70 | — |
| OAKDALE HEIGHTS ASSOCIATION, INC | 876 | 67 | — |
| HOPEVILLE POND S.P./BEACH-WELL #2 | 800 | 22 | — |
| INDIAN FIELD COOP CAMPGROUND ASSN., INC. | 685 | 223 | — |
| SALEM ELEMENTARY SCHOOL | 675 | 93 | — |
| SCWA, LEDYARD CENTER DIVISION | 652 | 43 | — |
| LISBON CENTRAL SCHOOL | 620 | 41 | — |
| PRESTON PLAINS WATER COMPANY | 550 | 120 | — |
| LEBANON ELEMENTARY SCHOOL | 525 | 686 | — |
| SCWA, CHESTERFIELD DIVISION | 524 | 2 | — |
| C E MURPHY SCHOOL | 520 | 217 | — |
| PRESTON VETERANS MEMORIAL SCHOOL | 500 | 45 | — |
| KITEMAUG ORCHARD ASSOCIATION, INC. | 490 | 168 | — |
| SCWA, HILLCREST DIVISION (HLC) | 450 | 11 | — |
| CTWC - SHORELINE REGION-MASONS ISLAND | 445 | 35 | — |
| CTWC - BAY MOUNTAIN | 440 | 326 | — |
| LEBANON MIDDLE SCHOOL | 415 | 245 | — |
| LYMAN MEMORIAL HIGH SCHOOL | 412 | 122 | — |
| AQUARION-ARLINGTON ACRES | 392 | 88 | — |
| SCWA, ROBIN HILL DIVISION (RBN) | 388 | 6 | — |
| SCWA, CEDAR RIDGE DIVISION | 370 | 116 | — |
| VOLUNTOWN ELEMENTARY SCHOOL | 365 | 12 | — |
| AQUARION-PLEASURE VALLEY | 328 | 30 | — |
| JEWETT CITY WATER CO., S & W SYSTEM | 320 | 39 | — |
| CLASSEE WATER SYSTEM - LATIMER POINT | 316 | 52 | — |
| PACHAUG MARINA CAMPGROUND | 310 | 74 | — |
| CHURCH OF CHRIST THE KING | 305 | 0 | — |