KNOCK KNOCK!
Who is it?
It's Physics, and it's pissed!
Not really. Liquid water has low viscosity, and unless you're brandishing an object in water with a high surface area, or the watch has a dissolvable sealant (which makes no sense), or you're able to swim with such a speed that individual water molecules cannot reorder themselves fast enough, harm should not befall the watch.
Again, no. The only significant change that occurs with water is a physical change- when water freezes. Since I assume the wearer will not be diving watch first into a block of ice, the watch should be ok.
The chemical properties of water do not change. A system that contains water may change depending on what is added/substracted to/from the system, but water does not change its properties. Thank physics this is true! And unless you're pondering to jump into a pool of concentrated acid or base, you shouldn't have much to worry about.
Actually it kind of is, for the reasons I stated above. However, an environmental condition outside of these constraints would warrant caution. Besides the unrealistic scenarios I posited above (acid/base bath, supersonic swimming speed, swimming within a block of ice) the only normally occurring activity within water that could harm an otherwise undefective Apple Watch would be deep water diving. Because of the large increase in pressure resulting from increased diving depth, divers would want to wear their pressure resistant watches instead of the Apple Watch for this task.
