Apple Watch Series 4 (GPS) requires an iPhone 5s or later with iOS 12 or later. Apple Watch Series 3 (GPS) requires an iPhone 5s or later with iOS 11 or later.
Apple Watch Series 4 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. However, Apple Watch Series 4 should not be used for scuba diving, waterskiing, or other activities involving high-velocity water or submersion below shallow depth.
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