So far, I am not impressed with Water. If you want my advice, don't get Water. Sure you can try to get her to work, but the other elemental mains outclass her immensely.
Get either lightning, fire, earth, or wind. I've seen some sick combos with lightning. I really like fire's splash damage and ignition effect. The ignition effect stops healing and inflicts some nice bonus damage - better than poison imo. Earth can be can incredible tank and frontline for your squishier, damage-dealing characters quite effectively. I've also seen some nice combos with the wind character. Her AoE rasengans and wind-based skills can really put a dent on common lightning characters such as Sasuke, Kakashi, and the lightning main character.