Watch Water Resistance Ratings Explained: ATM, BAR & What They Really Mean

What Water Resistance Actually Means

"Water resistant" is not the same as "waterproof". No watch is truly waterproof — the term has been banned from watch marketing by standards bodies for good reason. The water resistance rating printed on your dial or case back tells you the pressure the watch was able to withstand under static laboratory conditions — not what it can handle in the real world.

Real-world water exposure involves far more stress than a lab bench test. Splashing, the pressure wave created by a moving arm during swimming, the expansion and contraction caused by temperature changes, and the chemical effects of soap, chlorine, and salt water all attack the gasket in ways a static test does not replicate. And critically: that rating was accurate when the watch left the factory, with a fresh gasket. Gaskets age. The number on the dial does not update to reflect that.

ATM, BAR and Metres — The Rating System Explained

ATM (atmospheres), BAR, and metres are three ways of expressing the same thing: the static pressure the watch withstood during factory testing. One ATM equals roughly 10 metres of static water column. Here is what each rating actually means for everyday use:

The single most important thing to understand: the "metres" figure does not mean you can take the watch to that depth. It is a static pressure test value, not a diving depth rating. A watch rated to 50m has been tested at a pressure equivalent to a 50-metre water column while stationary — the dynamic pressure of a swimming stroke or a jump into water is significantly higher.

Why Hot Water and Steam Are More Dangerous Than Cold

Many people assume that a 10 ATM watch is safe for a shower. This is one of the most common misunderstandings we encounter. The problem is not the water pressure of a domestic shower — it is the temperature.

Thermal shock is what destroys watch seals. Metal case parts, the crystal, and the rubber or silicone gasket all expand and contract at different rates when exposed to heat. A hot shower or steam room creates rapid, repeated temperature changes that stress the gasket in ways cold-water pressure testing cannot replicate. Even a single hot shower on a 10 ATM watch can compromise the seal over time, and once the seal degrades, moisture enters.

If you must keep your watch on near water, use cold water only — and ensure the crown is fully pushed in (or screwed down on a screw-lock crown) before any exposure. An unsecured crown is an open door for water regardless of the ATM rating.

Signs Water Has Entered Your Watch

Water damage is not always immediately visible. Here are the four most common signs that moisture has breached the case:

What To Do If Water Gets Inside Your Watch — Immediately

Speed matters. The longer water sits in contact with the metal parts of a movement, the more corrosion forms — and corrosion is cumulative and largely irreversible without professional cleaning or part replacement.

1. 1
   Take the watch off immediately and do not operate the crown, pushers, or buttons. Moving any external control risks pushing water deeper into the movement, past seals that may still be partially intact.
2. 2
   Dry the outside with a soft cloth. Do not use a hairdryer — heat can damage the lubricants in the movement and may cause further thermal expansion of the case parts, pushing water further inside.
3. 3
   Do not leave it sitting in a drawer. Get it to a watchmaker within 24–48 hours. The longer moisture sits on metal parts, the more corrosion forms, and what could be a simple dry-out and gasket replacement becomes a full movement clean or parts replacement.
4. 4
   At the workshop: we dry the case, assess the movement for water damage, replace the gasket, and test water resistance before returning the watch to you. In most cases where the watch is brought in promptly, no movement damage has occurred.

How Often Should Water Resistance Be Tested?

The gaskets that create water resistance — typically made of rubber, silicone, or Teflon — degrade over time regardless of how carefully you treat the watch. UV exposure from sunlight, contact with sweat and chemicals, heat cycles, and simple age all cause the material to harden, shrink, and crack. As a general guideline, gaskets should be inspected every 1–2 years depending on how frequently the watch is worn and what it is exposed to.

Critically, the case back must be opened for every battery change and every service. Each time the case back is opened, the gasket seal is broken and must be reseated correctly. We check and replace the gasket as standard during every battery change and service at our workshop, and we offer a dedicated water resistance pressure test for watches where the owner wants confirmation of the seal before using the watch in water.

Tips to Preserve Water Resistance

• Always ensure the crown is fully pushed in (or screwed down on screw-lock crowns) before any exposure to water. An open crown bypasses every other seal in the watch.
• Do not operate pushers or the crown while the watch is wet or submerged. Any gap created by pulling or turning a crown while submerged allows water to enter under pressure.
• Rinse with fresh water after salt water exposure. Salt accelerates gasket degradation and metal corrosion. A quick rinse under cold fresh water after every sea swim significantly extends gasket life.
• Have the gasket inspected whenever the case back is opened — at every battery change or service. If your watchmaker does not mention the gasket, ask.
• Avoid steam, saunas, and hot tubs regardless of the ATM rating. Thermal stress destroys seals faster than water pressure does.

Frequently Asked Questions

Published by Iglisi Watch · Durrës, Albania · April 2026.