Our "tool" watches usually have a water resistance rating marked on them somewhere. The term "water resistance" is the liberal, politically correct version of the older and proudly unambiguous "water-proof". The rating is usually marked in meters - but it never says what kind of fluid those meters represent. Certainly, if I plunged my watch 200 meters deep into a pool of mercury I would expect something nasty to happen. However, we can safely assume that the Makers do mean water by the implication of references to swimming, diving, showering, etc. Other popular units of rating are "bars" or "atmospheres". All of these units are slightly different to each other, that is to say 10 bar is not exactly 10 atm. Similarly, 100m of seawater exerts a different pressure than 100m of fresh water. Here's a handy little table for those who just have to know.
It's used horizontally (stand up, fool!). Use the bold figures and go left or right to see the equivalents. For example, 10 bar is 99.291m of seawater. If yours is 20 bar then multiply the equivalent by 20/10, i.e. 2 x 99.291 = 198.58m. Divide by 0.3048 to get feet from meters . . 198.58/0.3048 = 652ft.
It looks like a watch rated in ATM is the most "water resistant" in theory but I have to say that, after taking some time to research and create this fine little table, I find it to be virtually useless! It's useless because it doesn't help anybody in the real world. In the real world, watches do not implode or flood with water as soon as the rating depth is exceeded, any more than Tritium lume becomes completely invisible exactly 12.33 years after it was made. Now warranties are a different matter, somewhat akin to falling buttered toast!