Water Resistance Explained

Water Resistant is a common mark stamped on the back of wrist watches to indicate how well a watch is sealed against ingress of water. It is usually accompanied by an indication of the static test pressure that a sample of newly manufactured watches was exposed to in a leakage test. The test pressure can be indicated either directly in bars, or (more commonly) as an equivalent water depth in meters (in the United States sometimes also in feet).

An indication of the test pressure[1] in terms of water depth does not mean a water resistant watch was designed for repeated long term use in such water depths. For example, a water resistant watch marked at 30 meters depth cannot be expected to withstand activity for longer time periods in a swimming pool, let alone continue to function at 30 meters under water. This is because the test is conducted only once using static pressure on some of the newly manufactured watches. The test for qualifying a diving watch for repeated usage in a given depth includes safety margins to take factors in account like aging of the seals, rapidly changing water pressure and temperature, as well as dynamic mechanical stresses encountered by a watch. Also every diving watch has to be fully tested for water resistance.

Watches are classified by their degree of water resistance which, due to the absence of official classification standards, roughly translates to the following (1 metre ≈ 3.29 feet):^[5]

Water resistance rating	Suitability	Remarks
Water Resistant or 50 m	Suitable for swimming, white water rafting, no snorkeling water related work, and fishing.	NOT suitable for diving.
Water Resistant 100 m	Suitable for recreational surfing, swimming, snorkeling, sailing and water sports.	NOT suitable for diving.
Water Resistant 200 m	Suitable for professional marine activity and serious surface water sports.	NOT suitable for diving.
Diver’s 100 m	Minimum ISO standard (ISO 6425) for scuba diving at depths NOT suitable for saturation diving.	Diver’s 100 m and 150 m watches are generally old(er) watches.
Diver’s 200 m or 300 m	Suitable for scuba diving at depths NOT suitable for saturation diving.	Typical ratings for contemporary diver’s watches.
Diver’s 300+ m for mixed-gas diving	Suitable for saturation diving (helium enriched environment).	Watches designed for mixed-gas diving will have the DIVER’S WATCH L M FOR MIXED-GAS DIVING additional marking to point this out.

Learn more about water-resistant classifications on Wikipedia.