Can I use the Apple Watch underwater?
Update (09/12/17): The Apple Watch Series 3 available September 22 is listed as "swimproof." The fine print on apple.com notes that the Series 3 Watch is water resistant up 50 meters under ISO standard 22810:2010. This means it is safe to take your watch in swimming pools or the ocean, but it should not be used for scuba diving, water skiing, or other water activities where it may be submerged in deeper water.
Yes, Apple Watch Series 2 is water resistant to a depth of 50 meters (164 feet). Watch OS includes swim-focused fitness tracking features developed specifically for these activities. Apple has designed the Apple Watch Series 2 for complete water immersion on a daily basis.
Series 2 has been discontinued.
On the other hand, the Apple Watch Series 1 is splash and water resistant, but not waterproof.
The Apple Watch Series 1 has a water resistance rating of IPX7 under IEC standard 60529. This means the watch will survive if you wash your hands while wearing it or if it gets caught in the occasional rain storm, but you should take it off when swimming.
Current Android Wear watches are made to IP67 standards. The IP Code (IP means "ingress protection") classifies electrical enclosures by the degree of protection provided. The first digit (6) means it is completely dust proof while the second digit (7) indicates water resistance.
With a rating of IPX7, Apple Watch Series 1 is water resistant to a depth of one meter (about 3.3 feet) for up to 30 minutes.