| SEATTLE PUBLIC UTILITIES | 1,091,904 | 29 | Clean |
| BELLEVUE CITY OF | 317,330 | 11 | Clean |
| KENT WATER DEPARTMENT | 166,421 | 37 | Detected |
| REDMOND WATER SYSTEM CITY OF | 163,335 | 2 | Detected |
| LAKEHAVEN WATER AND SEWER DISTRICT | 118,273 | 78 | Detected |
| HIGHLINE WATER DISTRICT | 115,950 | 9 | Clean |
| Auburn City of | 113,095 | 127 | Detected |
| RENTON CITY OF | 107,119 | 59 | Detected |
| NORTHSHORE UTILITY DISTRICT | 105,105 | 5 | Clean |
| SAMMAMISH PLATEAU WATER & SEWER | 79,362 | 77 | Detected |
| KIRKLAND CITY OF | 67,107 | 1 | Clean |
| SOOS CREEK WATER & SEWER DISTRICT | 64,534 | 1 | Clean |
| WOODINVILLE WATER DISTRICT | 59,873 | 5 | Clean |
| COVINGTON WATER DISTRICT | 52,276 | 21 | Detected |
| PORT OF SEATTLE/SEATAC AIRPORT | 49,483 | 14 | Clean |
| TUKWILA WATER DEPARTMENT | 45,374 | 0 | Clean |
| ISSAQUAH WATER SYSTEM | 43,584 | 257 | Clean |
| KING COUNTY WATER DISTRICT #20 | 38,974 | 3 | Clean |
| BOTHELL WATER CITY OF | 33,643 | 1 | Clean |
| North City Water District | 31,744 | 4 | Clean |
| MERCER ISLAND CITY OF | 30,689 | 8 | Clean |
| CEDAR RIVER WATER & SEWER DISTRICT | 28,671 | 0 | Detected |
| Lake Meridian Water District | 24,231 | 9 | Detected |
| ENUMCLAW WATER DEPARTMENT | 23,276 | 39 | Clean |
| KING COUNTY WATER DISTRICT NO 90 | 20,100 | 262 | Clean |
| KING COUNTY WATER DISTRICT #125 | 17,546 | 7 | Clean |
| KING COUNTY WATER DISTRICT #49 | 16,065 | 9 | Clean |
| COAL CREEK UTILITY DISTRICT | 15,989 | 12 | Clean |
| SNOQUALMIE WATER | 15,848 | 39 | Clean |
| SKYWAY WATER & SEWER | 12,036 | 4 | Clean |
| DUVALL CITY OF | 10,267 | 6 | Clean |
| UNION HILL WATER ASSOCIATION INC | 8,720 | 312 | Clean |
| NE SAMMAMISH SEWER & WATER DISTRICT | 8,516 | 19 | Clean |
| PACIFIC CITY OF | 7,925 | 16 | Clean |
| NORTH BEND CITY OF | 7,228 | 5 | Clean |
| SALLAL WATER ASSOCIATION INC | 6,600 | 15 | Clean |
| SNOQUALMIE PASS UTILITY DISTRICT | 5,805 | 322 | Clean |
| KING COUNTY WATER DISTRICT #54 | 5,037 | 20 | Clean |
| STEVENS PASS WATER SYSTEM | 4,053 | 35 | Clean |
| KING COUNTY WATER DISTRICT 119 | 3,796 | 3 | Clean |
| WATER DISTRICT 19 | 3,723 | 572 | Clean |
| AMES LAKE WATER ASSOC INC | 3,224 | 178 | — |
| ALGONA WATER DEPT | 3,180 | 13 | — |
| LAKE FOREST PARK WATER DISTRICT | 3,171 | 9,527 | Clean |
| FALL CITY WATER DIST. #127 | 2,987 | 15 | — |
| BLACK DIAMOND WATER DEPT | 2,420 | 194 | — |
| CARNATION WATER SYSTEM CITY OF | 2,400 | 12 | — |
| CHEROKEE BAY COMMUNITY CLUB INC | 2,400 | 25 | — |
| MIRRORMONT | 2,083 | 31 | — |
| HEIGHTS WATER | 2,051 | 6 | Clean |