I know my town has several public water spigots around... as another poster mentioned, near city parks. Like ball fields (soccer, base, etc). All the parks here have the big high pressure garden hose hydrants.
I've seen people with pickup trucks filling those HUGE truck bed mounted water tanks (the kind that takes the entire bed) from these hydrants (not city workers), so 50 gallons into an RV shouldn't raise an eyebrow.
The drinking water treatment facility has a big public hydrant out front too.
edit: Oh, if you have a generous budget, check out an atmospheric water generator ... gallons of 'free' drinking water a day.