What is backflow?

Backflow, or the reverse flow of contaminated water into a potable water distribution system, is caused by backsiphonage or backpressure.

  • Backsiphonage occurs when low pressure, or vacuum pressure, on the supply side of the connection causes water to be siphoned from the user sideback into the supply.
  • Backpressure occurs when increased pressure on the user side of the connection forces water into the supply.
  • Backflow can occur at residential, commercial, industrial or institutional cross-connections between potable and nonpotable water distribution systems.

Recommended Actions

  • The threat of deliberate backflow contamination necessitates vigilance and awareness on the part of water utilities and the public.
  • Water utilities should increase public awareness of the need to report suspicious activity around water facilities and provide public notification when scheduled work on distribution systems, hydrants and mains will occur.
  • Water utilities should ensure distribution system plans are stored in secure locations. Such information would allow individuals to understand where the system is most vulnerable.
  • Drinking water utilities should evaluate the feasibility of installing backflow prevention technologies to reduce the potential for cross-contamination.
  • Recipients should report suspicious incidents in the water sector to local water utilities immediately or the Water Information Sharing and Analysis Centers.  WaterISAC was created by the Association of Metropolitan Water Agencies as a confidential venue for sharing security vulnerabilities and solutions within the water industry.  Water ISAC can be reached at 866-H2O-ISAC (866-426-4722).

How to become a certified backflow tester
Missouri Backflow Prevention Regulations
Basics of Missouri Backflow Regulations -- PUB393
Backflow Prevention Frequently Asked Questions -- PUB 2158
Missouri Backflow Prevention -- PUB2016

Approved Backflow Assembly List

Regulation requires backflow prevention assemblies that are installed in Missouri to 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 all other devices on the USC or ASSE approved list are not considered containment devices in accordance with 10 CSR 60-11.010 and 11.030.
USC Approved Assemblies List
ASSE Approved Assemblies List

Backflow Prevention Assembly Testers

List of Backflow Prevention Assembly Testers
Backflow Assembly Test form 780-0804


American Society of Sanitary Engineering
American Backflow Prevention Association Tester Certification Information
Foundation for Cross-Connection Control and Hydraulic Research
U.S. Environmental Protection Agency Cross-Connection Manual
Drinking Water Security