| WORCESTER DPWP, WATER SUPPLY DIVISION | 206,518 | 47 | Detected |
| FITCHBURG DPW DIVISION OF WATER SUPPLY | 41,946 | 51 | Detected |
| LEOMINSTER WATER DIVISION | 41,683 | 345 | Detected |
| SHREWSBURY WATER DEPARTMENT | 38,325 | 25 | Detected |
| MILFORD WATER DEPARTMENT | 30,379 | 108 | Detected |
| WESTBOROUGH WATER DEPARTMENT | 21,567 | 147 | Detected |
| GARDNER WATER DEPARTMENT | 21,287 | 100 | Clean |
| SOUTHBRIDGE WATER DEPARTMENT | 19,180 | 24 | Detected |
| HOLDEN WATER DIVISION, DPW | 17,951 | 123 | Detected |
| WEBSTER WATER DEPARTMENT | 17,776 | 171 | Detected |
| CLINTON WATER DEPT | 15,530 | 53 | Clean |
| NORTHBOROUGH WATER DEPARTMENT (MWRA) | 13,535 | 432 | Clean |
| AUBURN WATER DISTRICT | 12,255 | 503 | Detected |
| UXBRIDGE DPW, WATER DIVISION | 11,525 | 55 | Detected |
| ASH/WIN JOINT WATER AUTHORITY | 11,394 | 1 | Clean |
| AQUARION WATER COMPANY, MILLBURY | 11,326 | 40 | Detected |
| GRAFTON WATER DISTRICT | 10,925 | 78 | Detected |
| SOUTHBOROUGH DPW WATER DIVISION (MWRA) | 10,514 | 17 | Clean |
| ATHOL DPW WATER DIVISION | 10,418 | 19 | Clean |
| BLACKSTONE WATER DEPARTMENT | 9,868 | 139 | Detected |
| WHITINSVILLE WATER COMPANY | 7,933 | 38 | Clean |
| NORTHBRIDGE WATER DIVISION | 7,889 | 23 | Clean |
| AQUARION WATER COMPANY OXFORD | 7,343 | 10 | Detected |
| LUNENBURG WATER DISTRICT | 7,145 | 28 | Detected |
| WEST BOYLSTON WATER DISTRICT | 7,132 | 163 | Detected |
| SPENCER WATER DEPARTMENT | 7,037 | 27 | Clean |
| STERLING WATER DEPARTMENT | 6,754 | 183 | Detected |
| TEMPLETON MUNIC. LIGHT AND WATER PLANT | 6,152 | 215 | Detected |
| HOPEDALE WATER DEPARTMENT | 6,017 | 68 | Detected |
| LANCASTER WATER DEPARTMENT | 6,000 | 49 | Clean |
| WINCHENDON WATER DEPARTMENT | 5,706 | 83 | Clean |
| RUTLAND WATER DEPARTMENT | 5,605 | 65 | Clean |
| DUDLEY WATER DEPARTMENT | 5,515 | 306 | Clean |
| STURBRIDGE WATER DEPARTMENT | 4,567 | 43 | Clean |
| UPTON DPW WATER/WASTEWATER DIVISION | 4,420 | 169 | Clean |
| DOUGLAS WATER DEPARTMENT | 4,400 | 64 | Clean |
| PAXTON WATER DEPARTMENT | 4,300 | 49 | Detected |
| BARRE WATER DEPARTMENT | 4,098 | 217 | Clean |
| NORTH BROOKFIELD WATER DEPARTMENT | 3,903 | 78 | Clean |
| WESTMINSTER DEPARTMENT OF PUBLIC WORKS | 3,741 | 34 | Clean |
| CHERRY VALLEY/ ROCHDALE WATER DISTRICT | 3,696 | 227 | Detected |
| ASHBURNHAM WATER DEPARTMENT | 3,680 | 214 | Clean |
| BOYLSTON WATER DISTRICT | 3,343 | 140 | Detected |
| SOUTH GRAFTON WATER DISTRICT | 3,262 | 45 | — |
| LEICESTER WATER SUPPLY DISTRICT | 3,200 | 184 | — |
| PILOT TRAVEL CENTER | 3,000 | 72 | — |
| WILKINSONVILLE WATER DISTRICT | 2,773 | 145 | — |
| WACHUSETT MOUNTAIN SKI AREA | 2,500 | 76 | — |
| WEST BROOKFIELD WATER DEPARTMENT | 2,477 | 58 | — |
| WARREN WATER DISTRICT | 2,289 | 28 | — |