The degree to which a watchcase can resist the intrusion of wetness is called its water resistance. Most watches sold have some ability to resist water. When purchasing a watch, look for the designation "water resist" to confirm that the watch has a specific level of resistance to moisture.

Water resistance of watches is rated based on a laboratory pressure tests comparable to a swimmer or diver sitting still at that pressure level. But many water-based activities involve a lot of movement and other environmental changes. These exceptions to how the watch was rated may challenge or defeat the water protection features of a water resistant watch.

In particular, the water resistance rating of a watch does not take in to account:

Sudden, rapid, and repeated water pressure changes or high water temperatures.

The ability of the watch to stay water resistant as it ages changes. The seals that prevent water from entering the watch will weaken and fail with age. For use in water, water resistant watches should be pressure checked every year. The seals should be replaced at least every two or three years.

There are several degrees of water resistance, and this information is shown in the product description for the watch you purchase.

Water resistance is specified in the depth of water measured in atmospheres, feet or meters. Here are common water resistance levels and the degree to which they protect your watch:

1 Atmosphere / 33 Feet / 10 Meters: A watch with this resistance level is protected against accidental exposure to water; for example, splashes, perspiration or accidental immersion. It should not be exposed to any water pressure.

3 Atmospheres / 100 Feet / 30 Meters: This level will easily withstand splashes or brief immersion in water. However, it is not sufficiently resistant for swimming.

5 Atmospheres / 165 Feet / 50 Meters: A watch with this level of resistance is wearable around household sinks, while playing sports and while swimming in shallow water. Do not wear it while scuba diving.

10 Atmospheres / 330 Feet / 100 Meters: This level of water resistance will allow a watch to be worn around household sinks, while playing sports and while swimming or poolside diving. Do not wear it while scuba diving.

15 Atmospheres / 500 Feet / 150 Meters: A watch with this resistance level is wearable around household sinks, while playing sports and while swimming or poolside diving. It is also suitable for snorkeling.

20 Atmospheres / 660 Feet / 200 Meters: This level of water resistance will allow a watch to be worn around household sinks, while playing sports and while swimming or poolside diving. It will also allow skin diving and scuba diving at depths not requiring helium gas.

The term "waterproof" was discontinued starting in the late 1960's. This change was brought about from several government organizations, including the Federal Trade Commission in the USA, who were investigating truthfulness and accuracy of product labeling and advertising.

"Waterproof" was considered to have misrepresented the products as more capable of preventing the entry of water under normal use circumstances than they were actually capable of. Specifically, diving-type watches never have been completely 'proof' of water entry under normal use and within the stated depth ratings. The seals that keep water out are not completely impervious and their effectiveness can be reduced over time with age, deterioration, and exposure to chemicals.

The designation "water resistant" is now used to describe such watches. There are no technical differences between a waterproof watch and a water resistant watch--they use the exact same methods and technologies to keep water out. The difference is only in what term was considered to appropriate to describe it at the time it was made.

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