There is a spigot at Fivemile Bar aka Buckskin Bill Museum and Store. Bring a few bucks for an ice cream bar or Root Beer Float too. They have jugs of ice for sale too (among other things that you would expect). I think we went through there on day 4 or 5.
I imagine some of the lodges have water fill up too, but not sure the protocol for that and whether they will let you or not. Most of the side creeks looked pretty clean and clear, but I wouldn't risk drinking straight out of the creek without boiling or filtering it.