We now have the final word on the water resistant rating of the Apple Watch thanks to the Watch design page of the online Apple store. The fine print located on the bottom of the page reads, "Apple Watch is splash and water resistant but not waterproof." It also says the watch has a "water resistance rating of IPX7 under IEC standard 60529".
This means it is safe to wear your watch when washing your hands or out in the rain but you should avoid fully submerging it in water. Apple also warns that its leather bands "are not water resistant."
There was some initial confusion about the water resistant rating of the Apple Watch after the French website iGen reported that Tim Cook told an Apple Store employee in Germany that he wears his watch in the shower. This led some to believe that the Apple Watch was waterproof, not water resistant. While it may be safe to wear your watch in the shower, you may want to familiarize yourself with the IPX7 water rating before jumping in.