It’s good to know that to ensure the good functioning of the watch it is fundamental to protect the case avoiding the entrance of external substances like dust, water and/or dirt so they don’t compromise its movement.
The water resistant indication qualifies a watch when its case is perfectly protected with washers, screw seals and other high performance systems.
Even vapour and hot water can be very dangerous because they damage and dilate the protective washers of the case.
The watches are declared “water resistant” by the Companies that produce them. A watch is declared “water resistant” if, and only if, at the end of a specific test its case doesn’t contain any traces of water. The test consists in closing the watch, one picked at random, in a special container and submitting it at a pressure of 2 to 3 bars (that respectively correspond to 20 and 30 metres in normal water pressure conditions).
We must point out that even if the watches are water resistant, in other words they resist up to “30 metres” ( almost all watches of the best brands are nowadays) they must absolutely not be immersed in water because the “water resistant” qualification will only indicate that the watch in question is able to offer a high resistance to the liquid element with which it only occasionally comes into contact with.
From this perspective, the “Water Resistant” indication on watches is to be mainly intended only as a guarantee of the good closure of the case.
A totally different matter is the “Waterproof” or “Diver”indication; to be declared as such by the companies that produce it, a watch must “individually” and not by random sampling, be able to resist at 100 metres (10 bars) under sea level and must also pass the absolute waterproof test in water at a 12.5 bar pressure, a value that is way above the 10 bar pressure it is guaranteed for.
This means that a watch is really waterproof only when it is guaranteed by the company that produces it to resist up to 100 metres under sea level.