Apple Watch Series 1 has a water resistance rating of IPX7 under IEC standard 60529. Apple Watch Series 1 is splash and water resistant, but submerging Apple Watch Series 1 is not recommended.
Apple Watch Series 2 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 2 should not be used for scuba diving, waterskiing, or other activities involving high-velocity water or submersion below shallow depth.