apple watch 3防水吗

Liquid damage not covered under warranty. And about Apple Watch Series 3, also on Apple.com: Apple Watch Series 3 has a water resistance rating of 50 meters under ISO standard 22810:2010. This means that it may be used for shallow-water activities like swimming in a pool or ocean.
水下50米，可以在游泳池和海水里用。建议海水里游泳出来后用清水清洗。或者你有买Apple care就不用管了。