Backflow Prevention, Cross-Connection Control, and Water Quality
Backflow Prevention, Cross-Connection Control, and Water Quality
This domain tests protection of potable water. Expect questions on air gaps, RPZ devices, test procedures, and water quality hazards.
Core rules
- An air gap is the best protection against backflow; it must be at least twice the effective opening of the supply pipe and never less than 1 in.
- Use an RPZ assembly for high hazards such as boiler feed, chemical injection, and irrigation with chemicals; use a DCVA for low hazards where backpressure is not possible.
- A PVB is for back-siphonage only and must be installed above the highest downstream outlet; an AVB is for low hazard, back-siphonage only, and cannot be under continuous pressure.
- Test reduced-pressure and double-check assemblies at installation and annually; tag the device and keep records.
- Protect against lead and copper corrosion, flush new systems, and control Legionella by managing hot water temperature and stagnation.
Worked example
A boiler is fed from the potable supply with antifreeze in the loop. The correct device is an RPZ, not a PVB, because the hazard is high and backpressure is possible. The RPZ relief port must discharge to a drain, and the assembly must be tested after installation.
Traps that cost marks
Using an AVB on a hose bibb with a shutoff downstream, installing an RPZ underground without a drain, skipping annual testing, and relying on a check valve as a backflow preventer.