| CAMBRIDGE WATER DEPARTMENT | 118,214 | 70 | Detected |
| LOWELL REGIONAL WATER UTILITY | 115,000 | 54 | Detected |
| NEWTON WATER DEPT. (MWRA) | 88,415 | 22 | Clean |
| SOMERVILLE WATER DEPT. (MWRA) | 81,045 | 33 | Clean |
| FRAMINGHAM WATER DEPT. (MWRA) | 72,362 | 12 | Clean |
| MALDEN WATER DIVISION (MWRA) | 66,263 | 45 | Clean |
| WALTHAM WATER DEPARTMENT | 65,218 | 35 | Clean |
| MEDFORD WATER DEPT. (MWRA) | 61,700 | 27 | Clean |
| EVERETT WATER DEPT. (MWRA) | 49,075 | 23 | Clean |
| ARLINGTON WATER DEPT. (MWRA) | 46,308 | 21 | Clean |
| BILLERICA WATER WORKS | 42,119 | 52 | Detected |
| MARLBOROUGH DPW WATER DIV. (MWRA) | 41,799 | 56 | Clean |
| WOBURN WATER DEPT. | 40,876 | 46 | Detected |
| NATICK WATER AND SEWER DIVISION | 37,006 | 146 | Detected |
| WATERTOWN WATER DEPT. (MWRA) | 35,329 | 19 | Clean |
| LEXINGTON WATER DEPT. (MWRA) | 34,074 | 17 | Clean |
| TEWKSBURY WATER DEPARTMENT | 31,342 | 30 | Detected |
| MELROSE WATER DIVISION (MWRA) | 29,357 | 45 | Clean |
| CHELMSFORD WATER DISTRICT | 28,750 | 12 | Detected |
| READING WATER DEPARTMENT (MWRA) | 27,358 | 7 | Clean |
| BELMONT WATER DEPT. (MWRA) | 27,295 | 11 | Clean |
| WAKEFIELD WATER DEPT | 27,090 | 113 | Detected |
| BURLINGTON WATER DEPT | 26,680 | 278 | Detected |
| DRACUT WATER SUPPLY DISTRICT | 25,789 | 114 | Detected |
| STONEHAM WATER DEPT (MWRA SUPPLY) | 23,244 | 33 | Clean |
| WINCHESTER WATER DEPT | 22,970 | 62 | Clean |
| WILMINGTON WATER DEPT | 22,481 | 65 | Detected |
| ACTON WATER SUPPLY DISTRICT | 20,780 | 174 | Detected |
| HUDSON WATER SUPPLY | 20,032 | 285 | Detected |
| ASHLAND WATER AND SEWER DEPT. | 18,832 | 45 | Detected |
| CONCORD WATER DEPT | 18,788 | 25 | Detected |
| WESTFORD WATER DEPARTMENT | 18,680 | 28 | Detected |
| SUDBURY WATER DISTRICT | 18,416 | 284 | Detected |
| NORTH READING WATER DEPT. | 16,054 | 61 | Detected |
| HOLLISTON WATER DEPARTMENT | 15,713 | 288 | Detected |
| BEDFORD WATER DEPT. | 14,394 | 137 | Clean |
| WAYLAND WATER DEPARTMENT | 13,196 | 101 | Detected |
| HOPKINTON WATER DEPARTMENT | 12,586 | 23 | Detected |
| WESTON WATER DEPT. | 11,941 | 33 | Clean |
| HANSCOM AFB | 11,789 | 41 | Clean |
| MAYNARD DPW, WATER DIVISION | 10,401 | 304 | Detected |
| KENWOOD WATER DISTRICT | 9,620 | 29 | Detected |
| LITTLETON WATER DEPARTMENT | 9,611 | 54 | Clean |
| PEPPERELL DPW WATER DIVISION | 9,217 | 141 | Detected |
| AYER DPW WATER DIVISION | 8,479 | 55 | Detected |
| NORTH CHELMSFORD WATER DIST | 7,498 | 14 | Detected |
| DEVENS MASSDEVELOPMENT | 6,500 | 49 | Detected |
| TOWNSEND WATER DEPARTMENT | 6,500 | 246 | Detected |
| LINCOLN WATER DEPT | 5,593 | 90 | Detected |
| GROTON WATER DEPARTMENT | 5,456 | 110 | Detected |