A cross-connection is any actual or potential physical connection between a drinking water system and any other non-potable substance (liquid, solid or gas). Premises isolation is the protection of the public potable water supply by the installation of a backflow prevention assembly immediately downstream of a water meter connection, isolating the public water distribution system from a customer's private water system. Backflow occurs when water or other substance flow in the opposite direction than intended, allowing contaminants to enter either public or private systems. Backflow incidents may cause injury, illness or death.
Backflow assemblies are devices installed on water service lines or at plumbing fixtures that prohibit the backflow of water. Two types of backflow prevention devices are commonly used to contain contaminants within service connections - the double check valve assembly (DCVA) and the reduced pressure backflow assembly (RPBA). Both types use check valves to prevent water from flowing backwards through the pipes.
The DCVA is a system used to prevent a cross-connection when the backflow would not be hazardous to one's health. The DCVA consists of a shut-off valve on either end and two check valves in the center. When water flows in the normal direction, the check valves are forced open by the flow of water.
The RPBA is more complex, adding a hydraulic spring-loaded pressure differential relief valve between the two check valves. This addition makes the RPBA suitable for cross-connection control where the backflow could create a danger to public health.
Washington State law requires backflow assemblies to be field tested annually to make sure the device is working properly. The District sends out notices to remind of upcoming reporting due in advance of due dates. Two documents, a form Backflow Prevention Assembly Test Report (PDF) and document Backflow Assembly Tester Resource List are provided in that notice. Should you have further questions or need additional information, please Email Chris Zoepfl, Cross-Connection Control Program Manager or call (253) 946-5427.