Backflow Prevention, Cross-Connection Control, and Potable Water Protection
What the exam tests
This domain tests cross-connection control: how contamination enters potable water, which backflow device fits the hazard, and how devices are tested and maintained.
Core rules
- Backsiphonage is caused by negative pressure; backpressure is caused by downstream pressure higher than supply pressure.
- An air gap is the highest protection. An RPZ is used for high hazards such as chemical injection, irrigation with fertilizer, and boiler feed with antifreeze.
- A double-check valve assembly is for low hazards; a pressure vacuum breaker is for low hazards where backpressure does not occur; an atmospheric vacuum breaker is not for continuous pressure.
- Hose bibbs need vacuum breakers. Devices must be tested at installation and annually by a certified tester, tagged, and kept accessible.
- Do not install a bypass around a backflow assembly.
Worked example
A commercial irrigation system injects fertilizer into the irrigation line. That is a health hazard, so a reduced-pressure zone assembly is required, not a pressure vacuum breaker. The RPZ must be installed above grade, protected from freezing, and tested annually. If the fertilizer injection were removed and the system were only irrigation, the hazard could be lower, but the AHJ still decides whether a PVB is acceptable.
Traps that cost marks
Using an AVB under continuous pressure; burying an RPZ; removing a device because it drips; failing to test annually; connecting a graywater or boiler line to potable water without protection.