Buried in the tiny print at the bottom of the Health and Fitness section of the Apple Watch site is a little tidbit regarding how well it can stand up to water:
Apple Watch is splash and water resistant but not waterproof. You can, for example, wear and use Apple Watch during exercise, in the rain, and while washing your hands, but submerging Apple Watch is not recommended. Apple Watch has a water resistance rating of IPX7 under IEC standard 60529. The leather bands are not water resistant.
What is IPX7? Well, a quick lookup on Wikipedia reveals that Apple Watch is rated to survive up to one meter of submersion for 30 minutes. That means that, if you’re reasonably careful, your bathtub or whirlpool aren’t out of the question. Still, if Apple says it’s not recommended, I wouldn’t try engaging in this stuff, but it’s nice to know that I don’t have to worry about getting Apple Watch wet during the course of normal day-to-day use. All of these hyped “shortcomings” sure seem to be coming up short.