Here’s the question I get more than almost any other: “My watch says 50 metres — can I swim with it?” The honest answer is: probably not the way you’re thinking. Water resistance ratings are one of the most consistently misunderstood specs in the watch world, and getting them wrong is a fast way to destroy a movement. So let’s sort this out properly.
No Watch Is Waterproof
The first thing worth clearing up is the language. “Waterproof” implies a permanent, unconditional seal — and no watch achieves that. Even the most serious professional dive watches are water resistant to a specific depth, under specific conditions, for a limited time. The Federal Trade Commission in the US actively discourages brands from using the word “waterproof” for this reason. So when you see it in marketing, treat it as shorthand for water resistant, not a guarantee.
What ATM, Bar, and Meters Actually Mean
All three — ATM (atmospheres), bar, and meters — describe the same thing: the amount of static pressure a watch was subjected to in a controlled laboratory test. For practical purposes, 1 ATM = 1 bar = 10 meters of pressure. They’re essentially interchangeable, with only negligible mathematical differences between ATM and bar. The critical word is static. The test involves holding the watch under steady, still pressure in a lab chamber. That is nothing like what happens when you’re swimming, diving, or jumping into water. Dynamic movement — your arm pulling through water, the impact of hitting the surface — creates pressure spikes far exceeding the static equivalent. A 50m-rated watch can fail at 1 meter depth if you dive in, because that impact pressure can momentarily exceed what the watch was tested to handle.
What the Ratings Actually Allow
This is where the myths live. Here’s what the numbers genuinely mean:
30m / 3ATM — Everyday splash resistance. Rain, washing hands, brief contact with water. Not suitable for swimming of any kind.
50m / 5ATM — Light swimming in calm, still water — a gentle pool session, for example. Not suitable for surfing, cliff jumping, high-impact water entry, or diving.
100m / 10ATM — Comfortable for general swimming and snorkelling. The minimum point where you can reasonably rely on the watch in recreational water.
200m / 20ATM — Proper dive watch territory. Suitable for recreational scuba diving. Most serious dive watches sit here.
300m+ — Professional dive territory, typically ISO 6425 certified.
The number that trips most people up is 50m. Half a dozen watch brands sell watches with this rating and describe them as suitable for swimming. Technically that’s accurate for controlled, calm-water swimming — but not for the way most people actually swim. Jump off a diving board, surf, or dive in at the deep end, and you’ve potentially exceeded the watch’s tested threshold in a single moment.
Water Resistance Degrades Over Time
Here’s something that doesn’t get mentioned nearly enough. That rating on your caseback applies to the watch when new. Water resistance isn’t permanent — it erodes over time, and the primary culprits are the rubber or silicone gaskets that seal the crown, caseback, and crystal.
Gaskets dry out, harden, and lose elasticity. They degrade faster with exposure to chlorine from swimming pools, salt from the ocean, heat from hot showers or saunas, soap, and even basic UV exposure over time. A watch you bought five years ago with a 100m rating may no longer reliably deliver that protection without a service. The recommendation is to have a watch pressure-tested every 1–2 years if you regularly expose it to water — and always after a battery replacement, since opening the case back disturbs the seal.
Three Rules Worth Keeping
Never operate the crown or pushers underwater. The crown is the most vulnerable point on any watch. Pulling or turning it while submerged creates a direct pathway for water into the movement. Always dry the watch and your hands before adjusting anything.
Rinse with fresh water after pool or ocean exposure. Chlorine and salt don’t just damage the exterior — they degrade the seals over time. A quick rinse after every swim adds real longevity.
Avoid hot water even on high-rated watches. Heat causes gaskets to expand unevenly and allows moisture to enter. A 200m dive watch in a hot shower is more vulnerable than a 50m watch in a cold pool.
The Practical Takeaway
If your watch says 30m — keep it dry. If it says 50m — brief, calm swimming only. If it says 100m or above — swim freely, snorkel comfortably. For scuba diving, you need 200m minimum with a screw-down crown. And regardless of the rating, get the seals checked regularly if you actually use that water resistance.
The number on the dial is a starting point, not a guarantee. Treat it that way and your watch will hold up. Ignore it and you’ll find out the hard way what a watchmaker charges to dry out a movement.
— Ethan
More ticks, more tales — Watchesfanboy
