| REGIONAL WATER AUTHORITY | 418,900 | 62 | Detected |
| WATERBURY WATER DEPARTMENT | 107,271 | 35 | Clean |
| MERIDEN WATER DIVISION | 58,441 | 119 | Detected |
| WALLINGFORD WATER DEPARTMENT | 37,267 | 188 | Detected |
| CTWC - SHORELINE REGION-GUILFORD SYSTEM | 33,975 | 575 | Detected |
| CTWC - NAUGATUCK REGION-CENTRAL SYSTEM | 22,735 | 15 | Clean |
| AQUARION-VALLEY | 13,080 | 26 | Detected |
| HERITAGE WATER COMPANY | 7,300 | 80 | Detected |
| WOLCOTT WATER DEPARTMENT | 2,550 | 137 | — |
| CTWC - LEGEND HILL SYSTEM | 1,368 | 118 | — |
| AQUARION-EAST DERBY | 1,101 | 32 | — |
| NONNEWAUG HIGH SCHOOL | 887 | 52 | — |
| SOUTHBURY TRAINING SCHOOL | 816 | 370 | — |
| ALCOTT SCHOOL | 638 | 108 | — |
| QUONNIPAUG HILLS - MAIN SYSTEM | 564 | 409 | — |
| BETHANY COMMUNITY SCHOOL | 550 | 0 | — |
| CALVARY FELLOWSHIP SOUTHBURY | 540 | 6 | — |
| MELISSA JONES SCHOOL | 484 | 79 | — |
| AMITY REGIONAL JUNIOR HIGH SCHOOL | 475 | 164 | — |
| HARMONY ACRES MOBILE HOME PARK | 465 | 232 | — |
| AQUARION-LAKESIDE | 455 | 165 | — |
| TYRRELL MIDDLE SCHOOL | 454 | 107 | — |
| AQUARION-OXFORD TOWNE CENTER | 449 | 6 | — |
| FRISBIE ELEMENTARY SCHOOL | 446 | 17 | — |
| QUASSY AMUSEMENT PARK | 431 | 15 | — |
| MIDDLEBURY ELEMENTARY SCHOOL | 412 | 90 | — |
| CAMP LAURELWOOD | 400 | 67 | — |
| 125-131 BRADLEY ROAD - WOODBRIDGE | 385 | 1,147 | — |
| THE COUNTRY SCHOOL (MAIN BUILDING) | 360 | 21 | — |
| THE LAKE HOUSE | 300 | 10 | — |
| ARROWHEAD BY THE LAKE ASSOCIATION, INC. | 288 | 117 | — |
| TRANQUILITY VINEYARD AND WINERY | 257 | 0 | — |
| SOUTH BROAD STREET SERVICE AREA | 250 | 9 | — |
| BLUE TRAILS WATER ASSOCIATION | 228 | 178 | — |
| CHURCH OF LATTER DAY SAINTS, WOODBRIDGE | 220 | 22 | — |
| COUNTRYSIDE APARTMENTS | 218 | 218 | — |
| AQUARION-CLEARVIEW HILLS | 215 | 8 | — |
| LATICRETE INTERNATIONAL | 200 | 347 | — |
| 171 AMITY ROAD | 180 | 246 | — |
| YMCA - CAMP MOUNTAIN LAUREL | 180 | 63 | — |
| CHURCH OF LATTER DAY SAINTS, MADISON | 172 | 0 | — |
| KETTLETOWN S.P./BEACH WELL | 167 | 34 | — |
| KETTLETOWN S.P./CAMPGROUND WELL | 167 | 27 | — |
| CHRIST THE SAVIOR ORTHODOX CHURCH | 150 | 116 | — |
| BETHANY MOBILE HOME PARK | 138 | 158 | — |
| IDLEVIEW MOBILE HOME PARK | 138 | 4 | — |
| CHILDREN'S VILLAGE - BOUNDLINE | 130 | 29 | — |
| GREAT EXPECTATIONS DAY CARE & ANNEX | 125 | 44 | — |
| NEW LIFE CHURCH - SOUTH RIDGE COMPLEX | 122 | 15 | — |
| CHURCH OF LATTER DAY SAINTS, SOUTHBURY | 121 | 7 | — |