Vampires and Full Submersion in water:

[dominantdrowess]

Obviously, if a vampire puts their hand in a window sill in direct daylight, it still burns its hand.

But?

Vampires can cross small streams without harm.
Vampires cannot fully submerse in water.

But? Etherealness - the protection against Implosion - could prevent a vampire from being fully submersed in water - and allow them, through knowledge of the magic system to unlock some of the content on the server. Just a weird "physics" interaction I thought about.

[The GrumpyCat]

I'm not really in favour of (effectivly) removing weaknesses from an already potentialy quite powerful class. If the balence team want to yell at me on this one, i'm open to having my mind changed, but I think for now this is going to be a 'No.'
Besides, I picture the water thing as very much a supernatural/magical issue, which physics doesn't have much to do with.
It's an interesting theoretical idea though, I'll give you that!