Almost everything, even the air, has moisture (read: water) in it. Water does reflect light-- haven't you ever seen your reflection in a pond before? Refracting light alone is an illusion, so imagine enemies being completely unable to locate you while you are underwater because your image is refracted all over. A shuriken doesn't have to be a star, it can be a needle or pin, not difficult to shape on the fly. In fact, icicles are one of the most common water elemental attacks in games. Assassination with a blade made of ice leaves no evidence after it melts. Having the ability to extract poisons from wounds would help you with safely using those poisons, and most poisons are water-based. Healing helps you pull off hit-and-run tactics, because you can escape, heal, and attack again before your opponent has recovered. If you can suck all the air out of someone, imagine how sucking all the water out of them would look. Water makes up about 60% of the human body, and removing even a portion of that can be fatal. In fact, their blood is mostly water, so you could take control of another person's body and frame them for the assassination. Steam rises, so you can transport yourself anywhere using a balloon. If your enemy is wearing clothing that can absorb water, you can easily increase their weight by over twenty pounds, slowing them down a great deal. You can then freeze them, stiffening their joints or encasing them in ice. Water also conducts electricity, and lightning is generated by clouds-- giant masses of floating ice crystals rubbing together to make static. Honestly, this is a silly argument. Just look at Naruto: there is an entire tribe for all of the cardinal elements and then some, and all of them appear equally ninja-esque to me. Wind would be my second choice anyway. Let's just leave this as a matter of personal preference and leave it at that, okay?