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.

• USC List of Approved Backflow Prevention Assemblies
• ASSE Product Certification

Backflow Prevention Assembly Testers

• List of Backflow Prevention Assembly Testers
• How to become a certified backflow tester
• Backflow Prevention Assembly Test Data and Maintenance Report - MO 780-0804

Resources

• American Society of Sanitary Engineering
• American Backflow Prevention Association Tester Certification Information
• Foundation for Cross-Connection Control and Hydraulic Research
• Drinking Water Security
• Rules of Department of Natural Resources Division 60—Safe Drinking Water Commission Chapter 11—Backflow Prevention
• Backflow Prevention - Frequently Asked Questions - PUB2158
• Basics of Missouri Backflow Regulations Community Water System - PUB0393
• Cross Connection Identification and Backflow Prevention Customer Fact Sheet - PUB2940
• Cross Connection Identification and Backflow Prevention Noncommunity Water System - PUB2941
• Missouri Backflow Prevention Assembly Tester - PUB2016
• Backflow Prevention Assembly Test Data and Maintenance Report - MO780-0804