I have a Water/Cold myself and I’m currently leveling a Water/Dark. /Dark and /Cold are amazing for bringing down tough targets. Cold I feel is more straight forward and Dark Miasma has a few more tools.
I myself love Water Blast (have them colored black like Shadows). I’m reading on here that it might be lacking in damage. However, with the debuffs from the 2 sets, their -regen and -resist, and Water Blast being fairly proc friendly… I think it could muster the damage. Maybe not as easily as Ice/Fire, but it can get there. I also feel it is much safer, with it’s added heal and the mitigation it provides with KD’s. @Darkir I believe has solo’d AV’s and GM’s with his Water Corruptor.