Actually, the FAA offers underwater egress training as a safety seminar. Around here it is offered in a high school pool, with a fake aircraft. You get will get totally wet, but it is good training. I first took a predecessor of this course about 35 years ago, when the Coast Guard offered it.
Look it up on the FAASTeam website, but here is an older link:
One thing I keep in mind is that most of the water I fly over is 42F in the summer and colder in the winter. Not quite as nice as a pool. But going through the training, even if you don't like it, is a good experience to have when one is evaluating risks of overwater flights.