What type of standard backflow prevention is required for a domestic bath?

• A. Type AUK2 air gap
• B. Type BUK2 air gap
• C. Reduced pressure zone
• D. Double check valve

Answer: (A)

Backflow prevention for a domestic bath relies on eliminating the possibility of water from the bath flowing back into the cold-water supply. The simplest and most reliable way to achieve this in a home fixture is an air gap—the water spout is separated from the bath surface by a vertical air space so any cross-connection cannot siphon water back into the supply.

The AUK2 air gap is the standard choice for a domestic bath because it provides that guaranteed physical break and is commonly approved by plumbing codes for residential use. It protects potable water from backflow regardless of pressure changes in the system.

The other options involve protective devices that are more suited to higher-risk or commercial scenarios or different fixtures. Reduced pressure zone devices and double-check valves add mechanical protection and complexity, which isn’t typically required for a standard home bath. The BUK2 air gap is another air-gap option, but the domestic bath standard specifies the AUK2 type for this fixture.