| AACRA Backflow Assembly Testing | 360-668-1117 | Woodinville |
| A-Bat Backflow Assembly Testing | 425-334-6423 | Everett |
| ABC Water Specialty Inc | 425-335-9826 | Lake Stevens |
| Advanced Irrigation Inc | 888-833-6220 | Pacific |
| Affordable Washington Backflow Testing | 425-892-4808 | Snohomish |
| Affordable Backflow Testers | 206-369-6178 | Renton |
| Always Testing Inc | 425-672-4345 | Mountlake Terrace |
| A-Plus | 425-830-3749 | Kirkland |
| Aqua Containment | 425-392-1523 | Issaquah |
| Aquasense | 425-881-8600 | Redmond |
| Auburn Mechanical | 253-838-9780 | Auburn |
| Available Backflow Testers | 425-652-9970 | Covington |
| A Women's Touch | 425-333-4934 | Carnation |
| BATman Testing | 206-228-1618 | Everett |
| Backflows Northwest | 425-277-2888 | Bellevue |
| Backflow Testing & Service | 425-334-3350 | Lake Stevens |
| Bat Master | 425-397-0275 | Lake Stevens |
| Budget Backflow Testing | 425-458-8272 | Bellevue |
| Certified Backflow Testing | 425-427-8889 | Sammamish |
| Combs Backflow Assembly | 425-736-4936 | Maple Valley |
| Dennis McLaughlin's Bacflow | 206-364-9531 | Seattle |
| Fire Chief Equipment | 425-641-2127 | Redmond |
| Froula Alarm Systems | 206-575-1962 | Tukwila |
| Malone's Landscape | 253-638-2080 | Covington |
| McLaughlins Peninsula Backflow | 206-890-8337 | Seattle |
| Mist'er Rain Inc. | 425-454-1190 | Bellevue |
| Mt Si Plumbing/Heating | 425-888-0433 | North Bend |
| Patriot Fire Protection | 253-926-2290 | Seattle |
| Olympic Landscaping And Irrigation Co. | 253-922-7075 | Puyallup |
| R.A. Brown Backflow Testing | 425-821-6801 | Kirkland |
| Redwood Backflow/Aardvark BF | 425-495-1939 | Redmond |
| Rodriguez Irrigation & Backflow Services | 425-765-6231 | Issaquah |
| Veteran Backflow Service | 253-792-9400 | Seattle |
| Winterbourne Landscape | 425-836-5193 | Redmond |