Jeremy C. from Singapore asks:
I love my dive watches, for the looks as much as the perceived toughness, and water resistance.
Now, I hardly even go near a swimming pool but that's not the point. One thing that irks me to no end, however, is that there seems to be no consensus on what water resistance ratings mean.
10 meters mean that I can't shower with it?!? 200 meters but not ISO-certified means that it shouldn't be used for diving? 1500 meters without a helium escape valve, and no special gaskets or case design? How is that possible?
What does it all even mean?!?! Please enlighten me. Thank you!
That is a good question and certainly a source of confusion for many watch wearers. To make a long story short, you are correct that the posted "water resistance" rating values can be deceiving and don't always translate into real world values (i.e. you can't really even get a 10 meter water resistant watch wet). This is a larger conversation but we will try to answer your questions.
First, we need to straighten out the units of measure.
Pressure gets measured in ATMs and is rendered as the easier-to-understand meters/feet on the dial, because we understand the depth in those terms and it's easy enough to convert atmospheric pressure to depth.
1 ATM is the surface. 33 ft is 2 ATM, adding 33 ft per ATM and so on. Meters to feet is 1m=3.28. Now that we have all the units of measure sorted out, I can answer the question about consensus on waterproof standards.
ISO set forth a few different standards for watches. The first, ISO 2281 Horology – Water-resistant watches defines the water resistance of watches. This standard was introduced in 1990, and covers watches that are casual, daily-wear pieces that should be fine for swimming, showering, and hand-washing, but aren't meant for the greater pressures and depths of diving. This standard covers immersion at 10 centimeters depth for an hour, and while pushing on pushers and the crown at that depth. It also contains a temperature shock test to test against condensation, and an overpressure test.
They also wrote a standard for dive watches, called the ISO 6425 divers' watches standard. This standard covers the much more extreme depths a dive watch can be subjected to. They start at 30cm, perform temperature shock, condensation testing, and overpressure at 125% of the rated pressure.
The problem with these ratings is that there's nothing that requires a watch manufacturer to comply with the ISO testing. The manufacturer may choose to do so, but it is not required. They could perform their own tests that are similar, or they could perform tests like the IP water resistance testing lays out: https://en.wikipedia.org/wiki/IP_Code - this sort of testing is commonly done for products like consumer electronics.
It is also important to note that many watches are "tested" not in water but in air pressure chambers, which is a bit different than how a watch would fare in the real world. Some watches are however test in water pressure tanks at the factory.
Yes, it may not be recommended to shower or swim with a watch rated to 30M or 3ATM, but this depends a little on the manufacturer as well. For example, the smartwatch manufacturers Meta and Pebble both rate their smartwatches at 3 or 5ATM (the dressier Meta Frame is rated at 3ATM) and it's fine to swim with them. As for the 1500M rated watch with no Helium Release Valve, it's probably a watch that was tested statically in a vacuum to that sort of pressure, but isn't one you'd practically use for diving, or diving that deep. Honestly, if I were diving (and I don't. Like you, I'm a desk diver) I would probably take a cheap, bright, reliable, legible watch as a backup to a dive computer. The most important part of the dive is coming back from it safely, not looking fashionable underwater.
As a quick guide to watch watch resistance we will say this. Watches which have a 30 or 50 meters water resistance are OK for activity such as washing your hands but not much more. At 100 meters of water resistance you should be able to swim in a pool without a problem. 200 meters of water resistance is OK for ocean swimming and activities such as snorkeling and most recreational diving which doesn't go down that far. A 300 meter water resistant watch can theoretically be used for professional diving assuming it is legible enough. Beyond that increased watch resistance rating of 500 meters, 1000 meters, or more aren't really useful to the majority of people on this planet. There are really about bragging rights, and while cool they aren't going to take you down to depths that you would travel as a human being.