Water Resistance

Water Resistance. The ability of the case of a watch to resist the intrusion of moisture is called its water resistance. Often times, a watch buyer will think that when he is buying a watch water resistant to 30 meters, he can swim with it since he wont be going deeper than 30 meters in any event.

Water resistance ratings of watches are a bit misleading. The water resistance rating of a watch is based on laboratory pressure tests comparable to 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 survive being lowered in still water to a depth of 30 meters. The other lesser know part is that, it is only certified to witstand the pressure of 30m, for a period of 90 seconds. 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, because the meter value does not reflect actual diving depth, but to air pressure.

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 used safely while swimming, I would recommend one with at least a 100 meter water resistance rating. This is fine for swimming or snorkeling 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 like jet-skiing or diving (without scuba gear) than at least a rating of 200 meters water resistant would be advisable.

Omega Seamaster Professioanl 300m/1000 feet (ft)

Going deep. For a diver, a watch with a 300m water resistance rating, would be the minimum recommended. The 300m rating may seem like overkill, but what does 300m water resistance really mean?

• Can withstand pressure equivalent to 300m of water depth, with the watch motionless in still water.
• Can be used for scuba diving to a depth 30m, for two hours.

A watch rated to 600m water resistance, can withstand pressure equivalent to a depth of 60m, for two hours. All of a sudden, the 1220m water resistance rating of the Rolex Sea Dweller does seem like the overkill it used to look like. Still, short of professional divers, a 300m rated Submariner should do fine.

Rolex Sea Dweller 1220m/4000ft

Remember that a watch has to follow the manufacturers prescribe service policy to retain its water resistance rating, so a unserviced watch water resistance will degrade over time.

Note: A watch with an ISO 200M water resistance rating would also be suitable for scuba diving.

Air-pressure. Water resistance rating is also useful in determining a watches ability to resist other pressures. If you intend to use a watch for any kind of non-water related sport activity from skiing to parachuting, a watch with at least 50 water resistance is required, and 100m would be recommended.