Apple has not officially designated the Apple Watch as either water proof or water resistant. If Mr. Cook actually said he wears his in the shower, it could indicate that Apple will market the device as one or the other.
The problem is the report is hearsay, and there could be some translation issues. It might even have been a joke. We have no context with which to judge this story. So don't invest too much in this rumor just yet.
In fact, I personally doubt the device is water resistant or proof. Even if the device is sealed, water and touch screens don't typically work well together at all. That would make it a coup for Apple—and if anyone could do it it is Apple—but I'm not expecting a water resistant or proof Apple Watch based on this anecdote.
Then there are the straps. Apple has plastic straps. but I wouldn't want to run the metal ones or leather through a shower.
Bah. I don't like this one at all.
In the meanwhile, Mr. Cook also reportedly says he charges his Apple Watch every night. This is in keeping with the very rough comments from Apple at the device's unveiling in September. At that time, we were told Apple had designed the watch to be charged at night, though the company was unspecific about how long it would actually run.
So yeah, I can believe that hasn't changed, but we still don't have context for the comments.