Are the contents of a bag of holding (such as scrolls) safe from water damage while inside it when the bag is immersed in water?
From the d20pfsrd.com entry:
If living creatures are placed within the bag, they can survive for up to 10 minutes, after which time they suffocate.
If you can suffocate in the bag, it is air tight. If it is air tight, it must be water tight. (Though, presumably, both of these conditions are incumbent upon the bag being closed.)