Section 10: CROSS-CONNECTION CONTROL AND BACKFLOW PREVENTION
Cross-Connections and Backflow. Cross-connections are the physical
links through which contaminated materials can enter a potable water supply. The
contaminant enters the potable water supply when the pressure of the polluted source
exceeds the pressure of the potable source. The flow of contaminated water to the
potable system is called "backflow." Backflow of contaminated water through cross-
connections can occur in all water systems and does occur in most water systems.
Backflow results from either back pressure or back siphonage. Backflow due to back
pressure occurs when the user's water system is under higher pressure than the public
water supply system. Back siphonage is caused by the development of negative or
sub-atmospheric pressures in the water supply piping. This condition occurs when
system pressure is lowered by pump malfunction or high fire flow.
References. Information on types of cross-connections, where cross-
connections occur, public health significance, methods of control, and details of setting
up a cross-connection control program can be found in the publications listed below:
AFI 32-1066, Plumbing Systems (par. 18.104.22.168)
Cross-Connection and Backflow Prevention (par. 2.2.39)
Manual of Cross-Connection Control (par. 2.2.53)
Manual of Water Supply Practices: Recommended Practice for
Backflow Prevention and Cross-Connection Control (par. 2.2.10)
Principles and Practices of Water Supply Operations Series:
Water Transmission and Distribution (par. 2.1.4)
Subsequent references to these publications use only the Section 2,
Applicable Documents, paragraph number noted above (in parentheses after the
Classes of Backflow Hazards. Backflow hazards have been divided into
the three classes--low, moderate, and high--as defined below. The Uniform Plumbing
Code recognizes two levels of hazard--low and high.
Class I--Low Degree of Hazard. If a backflow were to occur, the resulting
health significance would be limited to minor changes in the esthetic quality, such as
taste, odor, or color. The foreign substance must be nontoxic and nonbacterial in
nature, with no significant health effect.