If your watch says it’s water resistant up to 30 meters, that means you can dive down to 30 meters with it , right? Nope, you will destroy your watch that way. Although the dial or back of the case may give you a number, that number probably doesn’t refer to in-use scenarios — it is a reflection of a standardized water resistance classification. When in doubt, always lean towards the dry side.
If your watch doesn’t say it is water resistant, treat it as if it is a piece of paper. Water will do horrible things to it. If it does mention a vague sort of water resistance, still avoid getting it wet. A splash will be okay, but it is definitely not a good idea to go for a dip or shower with it on — especially since a hot shower’s steam will do even more horrible things to your watch.
Water Resistant 30 Meters / 3 ATM / 3 Bar
If your watch indicates that it is water resistant up to 30 meters, it actually means that it is just splash resistant. It does NOT mean that the watch will be fine if you bring it 30 meters below sea level. While it is certainly possible that your watch could survive an extremely brief trip under very careful conditions in extremely still water, you probably should not consider rolling the dice.
Water Resistant 50 Meters / 5 ATM / 5 Bar
If you’re watch indicates it is 50 meters water resistant, it means you can swim with it. However, you should keep its water exposure to a minimum. And by no means whatsoever, should you dive with it. 50 meters of depth will not do it any favours. Only push the buttons with your wrist above water.
Water Resistant 100 Meters / 10 ATM / 10 Bar
This is snorkeling territory. This watch has no problem living in the water for a while, and will even be fine on an extended snorkeling trip. Diving, however, should still be out of the question. Also remember to only push the buttons with your wrist above water.
Water Resistant 200 Meters / 200 ATM / 20 Bar
Though it might seem like it, this actually still is not dive watch territory. While 200 meters seems like a ton of leeway to scuba dive with, you should probably not even go down 10 meters. But by all means, do some laps in the pool with it on. But only push the buttons with your wrist above water.
Water Resistant 300 Meters / 300 ATM / 30 Bar
This is the dive watch territory, even though it hasn’t been certified to the ISO 6425 standard. You may dive with it.
Diver’s Watch or ISO 6425 Certified
If your watch has “ISO 6425” or “Divers” and then a depth number written on the dial or case, you have a watch designed for diving and certified up to a standard — unlike watches without ISO markings. This ISO standard means that the watch is guaranteed by the manufacturer to handle depths of at least 100 meters (if no number is given). Furthermore, all watches that measure up to this standard have significant shock, magnetic, and salt water tolerance. The ISO 6425 standard also provides an indication that the movement is running in total darkness. If you are going to go dive deep, go with one of these.
And remember, if your watch is vintage or you haven’t checked your seals in a few years, all bets are off until you get your watch checked.