I almost always fill my tank full. Unless I know for sure that I can hook up with my hose, and only if I know how good the water is. In some campgrounds, the water is not very good. Also even though some campgrounds say they have water, it might just be a pump several sites down. I don't want to carry water. So I like to have my own water. The only time I use the campground water is to put out fires, never with my own water unless there is none available. Hope this helps. I also carry a 5-gallons of my fresh water to use outside of the trailer. To drink, wash up, etc.
Travis