Apple Watch Series 3 (GPS + Cellular) requires an iPhone 6 or later with iOS 11 or later. Wireless service plan required for cellular service. Apple Watch and iPhone service provider must be the same. Not available with all service providers. Not all service providers support enterprise accounts; check with your employer and service provider. Some legacy plans may not be compatible. Prepaid plans are not supported. Coverage dependent on carrier network. Roaming is not available outside your carrier network coverage area. Contact your service provider for more details. Check apple.com/watch/cellular for participating wireless carriers and eligibility.
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. However, Apple Watch Series 3 should not be used for scuba diving, waterskiing, or other activities involving high-velocity water or submersion below shallow depth.