It can be done, but Apple says not to
Really enjoyed your photo walk of Balmy Alley in SF. Your models were just great.
So far as iphone underwater....a phone for almost any photography is an ergonomic disaster (not saying the results are bad, actually the photos, videos are excellent) underwater? No, hard to handle, hard to keep a hold of. In a swimming pool, sure. Swimming in the ocean, no way. Better off with a cheaper GoPro or one of the various digi cameras made for water use.
I enjoy your videos, photo walks, keep up the great work.