There’s no guarantee that The water resistance won’t fail. However, it is rated at 50 m water resistance, so it should be safe to use underwater, but with anything with soaps can deteriorate the water seals on the watch, Which you will want to make sure you rinse it off early when you’re through. Apple also recommends this off their website.
It shouldn’t be an issue, there are those who use their Apple Watches in hot tubs and don’t have problems. But again, its *not* a guarantee. The only thing I could also think of, is it steam can penetrate pass the water seals, that can be problematic.Just checking it will be ok in hot liquids. I probably wouldn’t go in the bath with it on but might dive in a really hot shower.