Yes, the armband is completely waterproof. However the strap is made of fabric, so it would be worth considering purchasing a spare strap if you plan to wear it in the shower, bath or pool frequently. These are available directly from Polar, and possibly on Amazon too! That'll prevent you having a damp armband during the day. 😄

Yes, however, after exposure to saltwater, it is important to clean the charging pins to prevent saltwater buildup.