State drinking water rules require public water systems to develop and implement cross-connection control programs to protect health. Under these programs, some water system customers (property owners) may have to install backflow prevention assemblies. Backflow assemblies must be tested (when installed and annually after that) to ensure they work correctly.

Washington State Department of Health (DOH) regulations require anyone who inspects, field tests, maintains, and repairs backflow prevention assemblies, devices, and air gaps that protect the public water system to pass the state's certification examination and maintain a valid certificate.

Below is a list of backflow assembly testers.