Looking for a non-toxic substance that evaporates very quickly
I'm assuming the answer is nope but if anyone has a genius idea for some way i could achieve this effect I would love to hear it.


Nope ;-)

Your concerns are justified and I wouldn't expose the audience to anything but water either.

you can 


use water from all above


and let the audience get wet
and hand out rain coats

use water and only let it rain to the left and right of a marked path or
apply a more sophisticated technique, as used by the random international art studio in their rain room. Here, it rains thoughout a whole room, but the visitors are tracked by cameras and whereever they move, the water is selectively switched off.