What is used to prevent contamination of a potable water system supplying a plumbing fixture such as a galley sink from a backup of sewage sanitary drains?

Correct Answer: Option B — Location of the potable water spigots above the rim of the galley sink.

To prevent back-siphonage or cross-contamination, potable water outlets must maintain an air gap. Locating spigots above the rim of the sink ensures that even if the sink overflows with contaminated sewage, there is no physical path for the waste to enter the potable water supply piping.