*groan* , technically true, yet useless answer!
I guess it depends, is my answer. If you've been to that campground before, and used the water, then likely it's fine.
Also remember unless you are getting some really high end microbial level filter, most filters are for sediment-type filtering. And some campgrounds might have really hard water, or taste funny (to you), so it all "depends".
If you're really concerned, don't hook up the hose right away. Let the water run for a bit from their tap, then fill a clear glass, and let it sit quietly for several hours, and see how much sediment there is, the smell, the taste, then decide to hook up or not.