The term “Waterproof” is often used to describe some watches, a more appropriate description is to call those watches “Water resistant” as they are unlikely to be waterproof in the true sense of the word.
Water resistant is a quality specification based on the definition of Standards organizations like ISO (International Organization for Standardization) and JIS (Japan Industrial Standards). It is commonly signified by a mark on the back of watches to indicate how well it seals out water. Also indicated is the static test pressure that newly manufactured sample of watches were exposed to in a leakage test. The test pressure can either in pressure units, such as the bar, atmospheres (atm) or as equivalent depth of the water in meters or feet.
Water resistant watches can be broadly divided into water resistant watch for daily use (test pressure indication is bars or atm) and diver’s watch (test pressure indication is meters or ft).
WATER RESIST 200m – 1000m:
The water resistance is as high as 200m – 1000m (water-resistant indications example: HE-GAS DIVER’S 300m). This watch is equipped with devices required for measuring the diving time and decompression time, such as a rotating bezel, can be used for deep-sea diving (mixed-gas diving) using the mixed gas of helium and oxygen for respiration.
WATER RESIST 100m – 200m:
The water resistance is as high as 100m – 200m (water-resistant indications example: AIR DIVER’S 100m) and longtime underwater use.
This watch is equipped with devices required for measuring the diving time and decompression time, such as a rotating bezel, can be used for shallow-water diving (scuba diving, etc.) using compressed air in a cylinder for respiration. This cannot be used for mixed-gas diving.
DAILY USE WATCH
ENHANCED WATER RESIST 10 BAR AND 20 BAR:
This can be used by people who do water sports (swimming, sailing, fishing, etc.,) and skin diving.
It is not advisable to use these watches for mixed-gas diving or air diving.
ENHANCED WATER RESIST 5 BAR:
This class of watches can be used by people who often touch water (fishery, agriculture, car washing, restaurants, etc.,) and who do water sports (swimming, sailing, fishing, etc.). They cannot be used for skin diving, mixed-gas diving, or air diving.
Even if the water resistance is 5 bars or more, avoid directly showering or applying tap water to it under high pressure.
WATER RESIST 2-3 BAR:
This can withstand perspiration, face washing water drops, rain, etc., in daily life, but cannot be used for water-using works, water sports, skin diving, and other types of diving.
Do not use it under conditions in which the water pressure changes sharply.
Finally, if your wristwatch has no marking of WATER RESIST on the case back, avoid direct contact of the watch with water.