Actually, near the Homestead, there's a natural spring (Jefferson Pool). The housing covering it is literally a run-down shack but the spring itself is pretty nice. Not the best to relax in though. (~ 6-7 ft deep? and no gradual decline. Seriously, it's a near-cylindrical hole in the ground.) That's the actual spring the Homestead indoor pool gets their water from.
http://www.virginiawind.com/virginia_travel/warm_springs.asp