Cross-Connection Control and Backflow Prevention
Core concepts
A cross-connection is any actual or potential connection between potable water and a contamination source. Backflow is reverse flow, caused by backsiphonage (negative pressure) or backpressure (downstream pressure exceeds supply). Know the degree of hazard: high hazard (health risk, toxic) vs. low hazard (aesthetic). Learn the devices: air gap (best, highest protection), reduced pressure principle assembly (RP/ RPZ), double check valve assembly, pressure vacuum breaker, atmospheric vacuum breaker, and hose-bibb vacuum breaker. Understand containment (at the meter/service) vs. isolation (at the fixture).
Program elements
Know that backflow assemblies require annual testing by a certified tester, registration, and records. Recognize common cross-connections: irrigation systems, boiler feed, chemical injection, hose bibs, pools, and fire sprinkler systems.
Traps to watch
- Recommending an RPZ for low hazard (overkill) or a double check for high hazard (unsafe).
- Confusing backsiphonage with backpressure.
- Forgetting that an air gap must have a physical separation, not just a valve.
- Missing the annual testing requirement and tester certification.
Rule of thumb / worked example
Match device to hazard: high hazard → air gap or RPZ; low hazard → double check or PVB (where applicable). If a chemical-injection system is connected to a potable line, that is a high hazard and requires an RPZ or air gap, tested annually.