Potable Water Protection, Backflow, and Cross-Connection Control
Hierarchy of protection
Backflow protection follows an order: an air gap is the only absolute protection, then the reduced-pressure principle assembly (RPZ), then the double check valve assembly, then the pressure vacuum breaker or atmospheric vacuum breaker for low-hazard, non-continuous pressure use. Hose bibbs take hose-connection vacuum breakers, and flushometer valves take integral or attached vacuum breakers.
Where protection is required
- Irrigation systems, especially with fertigation or a booster pump: RPZ.
- Fire sprinkler systems fed from a potable main: RPZ or double check, depending on hazard.
- Boilers, chemical dispensers, carbonators, photo processing: air gap or RPZ.
- Food-service equipment: air gap or approved receptor arrangement.
- Anything with a submerged inlet, hose connection, or chemical feed is a cross-connection until proven otherwise.
Testing and administration
Assemblies must be listed, installed in the manufacturer orientation with required clearances, and tested by a certified backflow tester at installation and annually afterward. Nevada water purveyors require test reports and maintain tester registration, and unauthorized removal of an assembly is a violation. Test tags stay on the assembly.
Worked example
A restaurant adds a carbonator fed from a potable line and proposes a single check valve. Rejected: carbon dioxide can pressurize the line and reverse flow, so an RPZ or an air gap is required, and the device must be tested and tagged.
Traps that cost marks
Using a double check where true backpressure exists, burying an RPZ in a pit subject to flooding, and confusing an air break with an air gap.