The truth. Depending on the context they will either report how many military veterans they employ (so just tabulation that goes to a checkbox if they bid for a government contract), or it involves military benefits in some manner, which will quickly come back to haunt you if you ‘lied’ on application docs.
It’s not just whether tap water is potable, it’s also about availability. My job gives us water in bottles because we’re mobile for 12 hours at a time, and nowhere near accessible water pipes. I guess I’m fucked.