Pressure is directly proportional to temperature and inversly to volume. P = KT/V
If the watch is good for 5atm/50m, will hot water raise the psi to damage it?

That's true of an ideal gas, but definitely not for water. Nevertheless, the pressure would certainly increase slightly as temperature goes up for a contained volume of water (i.e. if the watch was submerged inside a rigid container of fixed volume). In an open system, like the ocean or a lake or pool, however, where the water is free to thermally expand, I think the pressure would actually go down at 50m as temperature increased because the water's density would be slightly decreasing (and thus the weight of water pushing down from above would be less).

I was thinking about hot showers or hot tubs with mineral water

Aaah, I see. I guess it would have to be one heck of a hot shower to raise the pressure up to 5 atmospheres. ;)

I wasn't sure. Tanks

My typing is a little rusty

By the way, you can edit your posts if you switch to the old (V2) skin. It can be handy sometimes.

Of course the 5 atm/50 m limit refers to the watch's ability to resist EXTERNAL pressure. I would doubt that internal pressure would have any effect.