You'll have to ascertain whether they allow you to remain hooked up to their water supply or not. If not, then you hook up to water, fill your fresh water tank, and then immediately disconnect the hose and drain it.
In either case, you'd need to run your on-board heating system to make sure that your pipes and tanks stay above freezing. That, of course, applies to winterworthy RVs, ones whose tanks, pipes and valves are all inboard, insulated, and heated. If your tanks, pipes, and/or valves are exposed to the air, well, either you'll need to find a way to heat them, or you'd need just to use the rig winterized (i.e., no water use).
:)
Lynn
