The correct answer is B) Location of the potable water spigots above the rim of the galley sink. This is the correct answer because having the potable water spigots located above the rim of the galley sink prevents backflow and contamination of the potable water system. If the spigots were located below the rim, there would be a risk of sewage or other contaminants in the sink flowing back into the potable water supply, which could compromise the sanitation and safety of the water. The other options are incorrect because check valves (A) are not a sufficient safeguard against backflow, a P-trap (C) in the drain line only protects the drain itself, and locating the spigots below the rim (D) would actually increase the risk of contamination.