Water Elemental are the composite elemental - they combine a little bit of the best of all of the other elemental. Their strength is second only to an Earth Elemental (About equal to a Troll), their agility is good (About as good as an elf) and their HP are just under that of an Earth Elemental. They are the balanced elemental. Water Elemental also heal faster than any other elemental.
Level 50+ Water Elemental now have the Rogue ability to Backstab.