Backflow Prevention

What Is Backflow?

Backflow is the undesirable reversal of flow in a potable water distribution system through a cross-connection. A cross-connection is an actual or potential link connecting a source of pollution or contamination with a potable water supply. Backflow may allow liquids, gases, non-potable water and other substances from any source, to enter a public water system.

How Does Backflow Occur?

Backflow may occur due to backpressure or backsiphonage. Backpressure backflow is caused by a downstream pressure that is greater than the upstream or supply pressure in a public water system. Backsiphonage backflow is caused by a reduction in system pressure, which causes a sub-atmospheric pressure to exist in the water system. Backflow through a cross-connection can contaminate the potable water in a building, on a block, or throughout an entire water system.

What Is Backflow Prevention?

Backflow prevention protects public water systems from contamination or damage through cross-connections located in customer facilities. Backflow prevention is typically achieved by placing a backflow prevention assembly between the customer and the public water system. This is called containment backflow prevention.

Approved Backflow Assembly List

Regulation requires backflow prevention assemblies that are installed in Missouri be approved by either the Foundation for Cross Connection Control and Hydraulic Research at the University of Southern California or the American Society of Sanitary Engineering. Missouri only allows double check valve assemblies, reduced pressure principle assemblies, or approved air gap as containment devices. Therefore, other devices on the list are not containment devices in accordance with 10 CSR 60-11.010 and 11.030.