Every water system has cross-connections. Plumbing codes and State drinking water regulations require cross-connections to be controlled by approved methods (physical air gap) or approved mechanical backflow prevention devices or assemblies. The various types of mechanical backflow preventers include: reduced pressure backflow assembly (RPBA), reduced pressure detector assembly (RPDA), double check valve assembly (DCVA), double-check detector assembly (DCDA), pressure vacuum breaker assembly (PVBA), spill-resistant vacuum breaker assembly (SVBA) and atmospheric vacuum breaker (AVB). For a backflow preventer to provide proper protection, it must be approved for backflow protection, designed for the degree of hazard and backflow it is controlling, installed correctly, tested annually by a State certified tester, and repaired as necessary.
Visit the Washington State Department of Health's page on Cross-Connection and Backflow Prevention for more information.