Water Resistance Rating (Case Back) — What This Mark Means
A marking indicating the watch's tested water resistance depth, typically shown in meters, feet, bar, or ATM. This rating describes laboratory test conditions, not actual diving depth recommendations.
What This Usually Means
The water resistance rating tells you the static pressure the watch was tested to withstand in a controlled environment. A "100M" rating doesn't mean you should dive to 100 meters. Real-world conditions like arm movement, temperature changes, and aging gaskets significantly reduce effective water resistance.
Where to Find It
Usually printed or engraved on the case back, often around the perimeter or near the bottom. It commonly appears as "WATER RESISTANT 100M," "10 BAR," "WR100," or "W.R. 10ATM."
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Common Variations
Ratings are expressed in meters (50M, 100M, 200M), bar (5 bar, 10 bar, 20 bar), ATM (5 ATM, 10 ATM), or feet (330ft). Some watches simply state "WATER RESISTANT" without a specific depth, which typically indicates minimal splash resistance.
Common Misconceptions
The most common misunderstanding is treating the depth rating as a safe diving limit. A 50M-rated watch is generally only suitable for brief water exposure like hand washing, not swimming. Gaskets also degrade over time, so a rating from the factory may not reflect current water resistance.
What to Do Next
Have your watch's water resistance tested periodically, especially before any water activities. A watchmaker can perform a pressure test and replace gaskets if needed. Avoid operating the crown or pushers while the watch is submerged.
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Related Markings
A small symbol on the case back indicating it should be opened with a crystal press tool rather than unscrewed. This mar
WR 100M / 10 Bar MarkingA water resistance rating of 100 meters (10 bar/ATM), generally considered suitable for swimming and recreational water
Bar / ATM Pressure RatingA water resistance rating expressed in bar or ATM (atmospheres) instead of meters. One bar/ATM approximately equals 10 m
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Frequently asked questions
Does 100M water resistance mean I can dive to 100 meters?
No. The rating reflects static laboratory pressure tests. For actual diving, look for watches rated 200M or higher with ISO 6425 certification.
What does 'Water Resistant' without a depth mean?
It typically indicates the watch can handle minor splashes and rain but should not be submerged.
Does water resistance decrease over time?
Yes. Gaskets degrade with age, temperature changes, and chemical exposure. Annual testing is recommended for watches you wear around water.
Are meters and bar the same thing?
Not exactly. 1 bar is roughly equivalent to 10 meters of water pressure. A 10 bar watch is rated to approximately 100M.
Can I shower with a 50M water resistant watch?
It's generally not recommended. Hot water and soap can accelerate gasket degradation, and steam pressure can exceed the watch's resistance.
How can I get my water resistance re-tested?
Most watchmakers and service centers can perform a pressure test. It's typically inexpensive and takes only a few minutes.