It's also not too hard to refluff a lot of existing 4e mechanics. I played a Barbarian|Warden who was, to simplify a much more complicated relationship, possessed by a water elemental. So Form of Mountain's Thunder became Form of the Crashing Wave, while Guardian's Pounce became Geyser Strike (as she would jet across the battlefield leaving a geyser trail). Thundering Howl caused a wave to crash down following her sword.

Likewise, you can turn other powers into more water themed versions without touching the mechanics. A Wizard's Thunderwave might become Tidal Wave, a crash of water into of sound. Thunder damage still fits since big waves can be pretty damn loud, or you could grab a Frost Staff and switch it over to Cold, which is usually the damage type associated with water. Another PC I have is an Assassin with a Greatspear, and he has things like turning it into water to stab at a distance (Inescapable Blade, +2 reach and ignores cover) and growing barnacles where he strikes his foe's feet (Grave Spike, ongoing that knocks them prone)