The case,bezel,crown and crystal of a water-resistant watch are designed to keep out moisture. Watches have different levels of water resistance, as shown in the chart below. Match the degree of water resistance to the moisture conditions you want your watch to withstand. If you want to wear your watch while swimming, for example, a watch with a water resistance rating of 5 atmospheres (atm) or higher is a good choice.
*atm stands for atmosphere, a unit of measuring pressure.