Your watch says “100m water resistant” but the manual says don’t shower with it. What’s the point?
Good question. Water resistance ratings are confusing on purpose. Let me fix that.
The ISO Standard (Sort Of) #
ISO 22810 is the standard for watch water resistance. It tests static pressure, not real-world use. A watch rated 100m means it survived 10 bar of pressure in a lab for a few minutes. It does NOT mean you can dive to 100 meters.
Static pressure ignores movement, temperature changes, and the fact that turning a crown underwater can instantly flood the case. The ratings are conservative, but they’re also optimistic. Complicated.
Here’s what the numbers actually mean for daily use:
- 30m (3 bar): Splash resistant. Maybe light rain. Don’t wash your hands with it.
- 50m (5 bar): Swimming in a pool, maybe. I wouldn’t risk it. Rain is fine.
- 100m (10 bar): Actually swimmable. Shower-safe if the crown is screwed down. Don’t dive.
- 200m+ (20 bar): Proper dive watches. Do whatever you want.
I wore a 50m field watch to the gym once and forgot about it in the shower. Water got in within two days. Had to open the case, dry it out, replace the gasket. That watch now lives in a drawer.
Lesson learned: treat the rating as a minimum, not a promise.
Why Gaskets Matter More Than Depth #
Water resistance comes from gaskets - rubber rings that seal the case, crown, and crystal. Over time, they dry out, compress, or get contaminated with dust and oils.
Most manufacturers recommend servicing every 3-5 years. That includes replacing gaskets and pressure testing. If you skip it, your 200m dive watch might be a 30m dress watch and you won’t know until it’s too late.
I’ve tested this badly. Took a vintage Seiko diver (6309) into the sea without checking the seals first. It was rated 150m when new in 1984. By 2025, the gaskets were hard as plastic. Water got past the crown within 10 minutes at 2 meters depth.
Cost me €120 to service. Could’ve cost me the watch.
Screw-Down Crowns vs. Push-Pull #
Screw-down crowns add security. You thread them into the case, compressing a gasket. Push-pull crowns rely on friction and a single gasket. Both work, but screw-down is safer for anything above 100m.
The downside: you have to remember to screw it down. I’ve jumped in a pool with the crown unscrewed exactly once. The watch survived (200m diver, got lucky), but I felt like an idiot.
If your watch has a screw-down crown, check it before water exposure. Every time. It’s a habit you build or a repair bill you pay.
What About Showers? #
Hot water expands metal and contracts gaskets. Soap degrades rubber over time. Rapid temperature changes can crack old crystals or create negative pressure that sucks water in.
Is your 100m watch going to explode in the shower? Probably not. Will it last 10 years if you shower with it daily? Also probably not.
I shower with 200m+ watches and nothing else. Maybe that’s paranoid. Maybe I just don’t want to test it again.
Real-World Rules #
Here’s what I follow:
- Ignore 30m and 50m ratings. Treat them as “don’t get wet.”
- 100m is the minimum for swimming. Even then, screw-down crown preferred.
- Service every 3-5 years. Or pressure-test it annually if you swim often.
- Never operate the crown underwater. Even on a dive watch. Just don’t.
- Avoid hot tubs and saunas. Heat kills gaskets faster than water.
I’d rather be overcautious than deal with a fogged crystal and a dead movement. Water damage is expensive and often not covered by warranty - they’ll blame you for “misuse” even if you followed the rating.
The whole system is a bit of a scam, but those are the rules. Buy 100m minimum if you want to actually use the watch near water. 200m if you want peace of mind.
Or buy a G-Shock and stop worrying.
