The 7% brain part is just a myth thought https://en.wikipedia.org/wiki/Ten_percent_of_the_brain_myth, human use 100% of their brain. I know Vampires don't exist to begin with but at least try to come with a better explanation than a false information.
Increased brain power wouldn't explain the supernatural water manipulation powers either. I think the ending was too rushed (like the boring vampire apocalypse).