The exact meaning of the watch with 10 ATM water resistant is the watch can keep working at the 100M static water pressure. Because the waterproof test in the factory is static water pressure.
What you can do when wearing a 10 ATM watch? Simply you can wear it to swim, but not dive. Your arms are always swiping when swimming, so it is different from static water pressure. Waterproof 3 ATM watch is also called “life waterproof” and can only resist the washing and raining. Only waterproof 100 meters and above can be worn to swim. A 300 meter water resistant watch can be called a diving watch. Do not wear any watch to take sauna!
If one watch can be waterproof, the small rubber ring in the case back is key component. So the problem is: Rubber will age. When the watch is routinely maintained every four to five years, the waterproof rubber ring must be replaced. If it is not an official maintenance organization, you may not be able to get the original rubber ring.