Originally Posted by MoAlpha

Another problem with estimates of maximal water absorption rate is that hydration status has a big influence on it. A number from a study in well hydrated individuals is irrelevant.

Let me also say that caffeine is a weak diuretic, which loses its effect in the face of even mild dehydration. I once had to sit through a few hours of caffeine talk from people at the Army’s Soldier Systems Center in Natick, MA. They field trialed the hell out of it in elite operators doing terrible things for days on end and it increased performance with no effect on hydration.