Water resistance is stated as a depth (BAR, ATM, meters or feet). It represents the fact that this model was tested in a laboratory to withstand the static pressure for a short period of time, only at the stated depth. Remember that when you actually use the watch, you are putting it under more water pressure than the static pressure. For example, if you dive into the water, the impact on the watch is far greater when it hits the water surface than the pressure when the watch is resting on your wrist underneath the water.
Not marked. If your watch is not marked water resistant, you should take it off before you wash your hands, take a shower or wash the dishes.
If the watch is marked water resistant, but no specific numbers are given, it can withstand an accidental splash experienced when you run in the rain from your car to your house. It is not safe to wear it when washing your hands or showering.
If it is labeled water to 3 ATM, 30 meters and 100 feet, the watch is suitable for accidental splashes. You can wear it to wash up, but not when you go swimming.
If it is marked water to 5 ATM, 50 meters and 165 feet, you can wear it while swimming, but not when you are diving in a pool, snorkeling or engaging in water sports.
If it is marked water resistant to 10 ATM, 100 meters and 330 feet, you can wear it to swim and snorkel. But it is not safe for diving off the high board or sub-water diving.
If it is marked water top 20 ATM, 200 meters and 660 feet, it is capable of withstanding all high-impact water sports and scuba diving at depths not requiring helium gas.
The water resistant standard was set in 1990 by the International Organization for Standardization – the same group that banned the use of the term waterproof to describe watches. The standard spells out the testing procedure for each mark. It establishes pressures, test duration, water temperature and other factors.
The testing for water resistance consists of testing:
the watch’s resistance when immersed in water at a depth of 10 cm for one hour
resistance of the watch’s operative parts when immersed in 10 cm of water with a force of 5 N for 10 minutes
Condensation test – done by placing the watch on a plate heated to 40°C to 45°C for about 10 to 20 minutes; testers then place a drop of water on the glass of the watch and look for any condensation on the interior of the glass after one minute
Resistance to different temperatures by immersing the watch in 10 cm of water for five minutes at different temperatures
Resistance to water overpressure by immersing the watch in a suitable pressure vessel and subjecting it within 1 minute to the rated pressure for 10 minutes, etc.
Resistance to air overpressure by exposing the watch to an overpressure of 2 bar; the watch should not show air-flow exceeding 50 µg/min