Water shield, does it need a nerf?

The more i play against combos Warr+Shaman in 2v2 or +something in 3v3 the more i realize how important ability this is. Shamans (i mean restoration Shamans ofc) wouldn't last and do anything without it. I play Druid+Lock and Hunter+Priest and every time we ran into Shamy healer he gets his mana drained almost instantly (less than 1minute) but then pops on Water Shield and what happens? Most of Shamans are able to run around, heal himself and his teammate with no problems for another 10minutes with no more than 300-600 mana in his mana pool. As hunter i dispell it he pops on another one, pet hits twice i hit once and he has 750 mana, enough to heal him to full hp...

Im just wondering whether ability with no mana cost, no cooldown but huge mana regenerating abilities is normal in pvp and arena battles in general...Thx