I fill mine at home before we leave since our city water is quite good (no hard water crust on things, tastes good). On the few occasions we’ve done winter camping so far the RV stayed winterized so it didn’t get filled in the first place. We made the trek to the shower houses to use the toilets there. This year we might try using water but I’m paranoid about freezing pipes and holding tanks since we don’t have heaters for them. I’m imagining the water is going to be turned off at the dump station but this is normally where you fill up at the park. At least at our state park stations in Michigan, the water runs up tall pole with a dangling hose and there’s no way that’s not freezing solid in the cold.