hello, friend! why are you worried about the sink? the bowl doesn't touch the sink, right? how dirty are your roommates and the bathroom where you think this is an issue?
if your tap water (and, apparently, sink) is safe for you to drink from, then it is safe for your snakes. all my snakes get tap water from my bathroom sink.
EDIT: granted, i don't go licking my sink every day, but worrying about filling up water bowls from it isn't an issue for me.
EDIT 2: clean the sink regularly??