One thing I've never seen answered. Is just a splash 
permanent, or does 
it require a whole dunking?

--John

Good question.  I can't recall seeing anyone getting
splashed in the manga, but can tell you this:

Mousse brought Spring of Drowned Duck water to Nerima,
and attempted to curse Ranma/Akane with it.  Evidently,
he believed that the effects would be permanent.

June (KaraOhki)