Surface wash systems must have a/an ________ vacuum breaker or a reduced pressure principle backflow assembly in the supply line.

A surface wash system is designed to prevent contamination of drinking water supplies by ensuring that no backflow can occur from the surface wash system into the potable water lines. The use of a vacuum breaker or a reduced pressure principle backflow assembly plays a critical role in this safeguarding.

An atmospheric vacuum breaker is specifically designed to prevent back siphonage, which can happen when there's a drop in water pressure in the supply line. By using an atmospheric vacuum breaker, the system ensures that when the pressure in the supply line drops, air enters the system rather than allowing contaminated water to be siphoned back into the clean water supply. This effectively protects the potable water system from becoming contaminated.

While the other options may refer to different types of mechanisms used in various plumbing systems, they do not fulfill the same function as the atmospheric vacuum breaker in the context of backflow prevention for surface wash systems. Thus, the atmospheric vacuum breaker is the most appropriate and effective choice for ensuring the safety of the drinking water supply related to surface wash systems.