Water Resistance for watches and what they mean

30 Meters Water Resistance, 1 ATM, 100 feet water resiatnce? What do they mean?

Water Resistance is the ability of the case of a watch to resist the intrusion of moisture.

Often when we buy a watch water resistant to 30 meters, we think we can swim with it since we won't be going deeper than 30 meters in any event.

Water resistance ratings of watches are aquite difficult to understand. The water resistance rating of a watch is based on laboratory pressure tests. It is conducted by gently lowering that watch into still water to the certified depth.For example, when a watch is rated water resistant to 30 meters or 3 ATM (3 atmospheres), it means that it can withstand the water depth after being lowered in still water to a depth of 30 meters.

In addition, it is only certified to witstand the pressure of 30m, for a period of one and a half minutes. It is tested for be resistant to water for a period of 30 minutes at the pressure equivalent to a depth of 1 meter.Why? That's because the meter value does not reflect actual diving depth, but to air pressure.

During actual usage, we dive in pools or at least wade about in water. Diving into a pool or moving your arms in a freestyle motion while swimming creates more pressure than that found in still waters 30m below the surface. For all practical intents and purpose a watch with 30m water resistance should simply be not used in the water. Think of it as more of protection against accidental exposure to water. I would recommend that you do not even let it get hit by a direct flow of water from a household sink.

For a watch to be really used for swimming, I would recommend one with at least a 100 meter water resistance rating. This is fine for swimming or snorkelling close to the surface, but not for any kind of diving. If you are buying a watch to be used specifically for use with water sports or diving (without scuba gear) than at least a rating of 200 meters water resistant would be advisable.