He DOES take damage from running water.
I understand letting run around in sunlight both because the sunlight killing vampires thing is mostly only a thing from the movies and because it would be untenable from a gameplay standpoint.
It's also implied in some dialogue (can't recall where, right now) that sunlight does hurt vampires, but the tadpole somehow suppresses this downside of his vampirism.
The running water things was a nice toch, I was grinning like mad when I noticed it.
