The international standard ISO 2281 Horology--Water-resistant watches defines the water resistance of watches. This standard was only designed for watches intended for ordinary daily use during exercises under water for a short period under conditions where water pressure and temperature vary.
The international standard ISO 6425-Divers' Watches defines such watches as: A watch designed to withstand diving in water at depths of at least 100 m and possessing a system to control the time. Diving watches are tested in static or still water under 125% of the rated (water) pressure, thus a watch with a 200 meter rating will be water resistant if it is stationary and under 250 metres of static water. The testing of the water resistance is fundamentally different from non-diving watches, because every watch has to be fully tested.
Watches are classified by their degree of water resistance, which due to the absence of official classification standards, roughly translates to the following (1metre≈3.29 feet):
|Water Resistance Rating||Suitability||Remarks|
|Water Resistant or 30m||Suitable for everyday use. Splash/rain resistant. NOT suitable for swimming, snorkeling, water Related work and fishing.||Not suitable for diving|
|Water Resistant 50m||Suitable for swimming, white water rafting, no snorkeling water related work, and fishing.||Not suitable for diving|
|Water Resistant 100m||Suitable for recreational surfing, swimming, snorkeling, sailing and water sports.||Not suitable for diving|
|Water Resistant 200m||Suitable for professional marine activity and serious surface water sports.||Not suitable for diving|
|Diver's 100m||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.|