| OXNARD WATER DEPT | 200,232 | 14 | Detected |
| VENTURA WATER DEPARTMENT | 113,500 | 12 | Detected |
| VENTURA WWD NO. 8 - SIMI VALLEY | 94,738 | 12 | Clean |
| CAL AMERICAN WATER CO | 66,809 | 10 | Detected |
| CITY OF THOUSAND OAKS WATER DEPARTMENT | 53,157 | 0 | Clean |
| CAMARILLO WATER DEPT | 46,824 | 0 | Detected |
| GOLDEN STATE WATER COMPANY - SIMI VALLEY | 45,128 | 0 | Detected |
| VENTURA CWWD NO. 1 - MOORPARK | 35,514 | 0 | Detected |
| CAMROSA WATER DISTRICT | 32,700 | 7 | Detected |
| CITY OF SANTA PAULA | 31,018 | 4 | Detected |
| PORT HUENEME CITY WATER DEPT | 21,407 | 16 | Detected |
| CALIFORNIA WATER SERVICE CO - WESTLAKE | 19,533 | 0 | Detected |
| FILLMORE WATER DEPT | 16,419 | 13 | Detected |
| TRIUNFO WATER & SANITATION DISTRICT | 13,898 | 11 | Detected |
| CASITAS MUNICIPAL WATER DIST | 11,005 | 20 | Detected |
| NAVAL BASE VENTURA COUNTY, PORT HUENEME | 8,625 | 14 | — |
| OJAI WATER SYSTEM | 6,801 | 4 | Detected |
| VENTURA RIVER WATER DISTRICT | 6,100 | 10 | Detected |
| NAVAL BASE VENTURA COUNTY, POINT MUGU | 5,700 | 14 | — |
| PLEASANT VALLEY MUTUAL WATER CO | 5,000 | 9 | Detected |
| CHANNEL ISLANDS BEACH CSD | 4,560 | 0 | Detected |
| MEINERS OAKS CWD | 4,200 | 23 | Detected |
| SMITH FORKS WATER SYSTEM | 3,000 | 2 | — |
| RIO MESA HIGH SCHOOL/OXNARD UHS | 2,600 | 8 | — |
| CRESTVIEW MUTUAL WATER CO | 2,079 | 7 | — |
| CAL AMERICAN WC - LAS POSAS ESTATES | 2,039 | 0 | — |
| CAL AMERICAN WATER COMPANY - PIRU | 2,003 | 6 | — |
| VENTURA CWWD NO. 17 - BELL CANYON | 1,946 | 0 | — |
| VINEYARD AVENUE ACRES MWC | 1,820 | 12 | — |
| VENTURA CWWD NO. 38 - LAKE SHERWOOD | 1,759 | 0 | — |
| CAL AMERICAN WC - RIO PLAZA | 1,709 | 11 | — |
| VENTURA CWWD NO. 19 - SOMIS | 1,429 | 2 | — |
| GARDEN ACRES MUTUAL WATER CO | 1,335 | 16 | — |
| VINEYARD AVE ESTATES MWC | 1,200 | 8 | — |
| LIMONEIRA RANCH #1 | 1,187 | 6 | — |
| DEMPSEY ROAD MUTUAL WATER CO | 990 | 3 | — |
| RIO MANOR MUTUAL WATER CO | 983 | 20 | — |
| NYELAND ACRES MUTUAL WATER CO | 975 | 53 | — |
| LAKE PIRU PARK - UWCD | 960 | 28 | — |
| RIO SCHOOL DIST/RIO DEL VALLE SCHOOL | 820 | 15 | — |
| SENIOR CANYON MUTUAL WATER CO | 800 | 42 | — |
| CROWN POINTE ESTATES AT MALIBU, LLC | 690 | 11 | — |
| BRANDEIS BARDIN INSTITUTE | 665 | 14 | — |
| RANCHO SESPE WORKERS IMP ASSOC | 600 | 16 | — |
| GLASS HOUSE CAMARILLO CULTIVATION, LLC | 600 | 12 | — |
| RIO SCHOOL DIST/ RIO REAL SCHOOL | 550 | 12 | — |
| USFS - WHEELER GORGE CAMPGROUND | 500 | 50 | — |
| THOMAS AQUINAS COLLEGE | 472 | 13 | — |
| CLOVERDALE MUTUAL WATER CO. | 455 | 8 | — |
| STRICKLAND MUTUAL WATER COMPANY | 429 | 78 | — |