Pretty much any liquid will help rehydrate you, but those that contain caffeine are not going to work as well. Sports drinks can actually work better than water if you are really dehydrated (the electrolytes help keep the liquid in your body longer and give you more time to absorb it).
I can say that I've pretty much reversed the condition with L-lysine supplements (2000 mg divided AM/PM) and a stress-formula B-complex (just once a day). I only developed the problem last year, so it might have a different root cause than yours.
A product made specifically for lip exfoliation might be better than a pumice stone :).