patch 2.4 has been on the PTR. A change was made such that if you sat down to drink, and drank for less than five seconds, you would receive a reduced benefit -- i.e., less mana. The assumption was that this nerf was made to combat people regenning mana too fast in the Arenas, which led to objections to the change being applied to PvE situations as well.
European US CM Bornakk replied that in most cases we'd be drinking more than five seconds in PvE situations, and players responded with many counterexamples (chain pulls, etc.). Bornakk replied to that saying basically that he still thought it wouldn't be hard to drink long enough to avoid the change's effects, and that the change was meant to effect "more than just Arenas" anyway. Well, it looks like they've changed their mind: Kalgan himself just announced that the water nerf will now only affect Arenas. PvE casters rejoice!