Ah, thank you. I was afraid that it was something like that, and am a little concerned about those names meaning little to readers (the Egyptian name especially). I'll think on it, but I may end up simply describing the thing and having done with it.
Thank you for the help! ^_^
Actually, I'd be inclined to give vampires difficulty in learning water-magic, given the traditional trouble that such creatures could have in crossing running water.
They might, however, use it as Killer Clowns suggests, in corrupted form: they have power over stagnant water, and vampire mages can force running water to stagnate, both in order to harm others (via disease or drought) and in order to allow them to cross.
(Of course, your vampires may not have the "crossing running water" weakness, but I still think that pure, vital running water seems ill-suited to vampires.)
As to affinities, I'd suggest earth (death, stagnancy, the grave), and perhaps echo Killer Clowns in suggesting "cold". The corrupted water magic suggested above might work by forcing water magic to behave as earth magic, twisting it away from its true nature.