Watches Take the Plunge: Understanding Water Resistance

By Vincent Bergerat, Creative and Design Director at Kelton.

Reading time: 7 minutes.

Divers, ATM, meters, bars… the mysteries of water resistance finally revealed!

Is your watch water-resistant or actually ready for scuba diving? There's a dizzying gap between 30 meters, which is only good for surviving rain, 50 meters, which allows for breaststroke, and 200 meters, which truly takes you into deep waters. We'll explain, without jargon or floats, how your timepiece handles water pressure—and what you can really put it through this summer.

Water Resistance: Explained.

Before diving in, let's take a look at the small print on the dial. Just below the hands' axis, there's usually an indication—often mysterious—about your watch's relationship with water.

You might see a certain number of ATMs (atmospheres), bars, meters, or a not-so-clear indication like "Water Resistant." Is your watch truly waterproof then? There are many ways to indicate whether or not you can jump off the boat into the sea or if you'll need to entrust your Kelton to a reliable person who will stay dry.

A little spoiler: "water resistant" on its own, without a number, doesn't mean much. It's the "bon appétit" of watchmaking: pleasant, polite, but completely non-committal. A splash-resistant watch will survive rain and when you wash your hands; it won't survive a cannonball from the dock. The nuance lies in a number, and that number changes everything.

What is water resistance?

To be perfectly clear, a watch's water resistance is its ability to withstand pressurized water, yes. But how do you prevent water from getting in? Thanks to O-ring gaskets* placed at the three possible entry points: the crystal, the case back, and the crown (the winder).

Three doors, three locks. The crystal is pressed or screwed onto the case, the case back is screwed or snapped on, and the crown—the most vulnerable of the three, as it's the only one that moves—seals everything. At each interface, a compressed rubber gasket acts as a barrier: the deeper you go, the more the water pressure presses these gaskets against their housings. A well-designed watch is therefore paradoxically more watertight the deeper it is taken.

It should be noted that a screw-down crown is highly recommended for sports watches; it screws and unscrews, providing optimal water resistance at this specific point. It should also be mentioned that a watch's water resistance is, unfortunately, not eternal; it evolves and can degrade, for example, after an intervention (battery change or repair).

The gaskets themselves age: they dry out, compress, lose their elasticity. Add salt, chlorine, sunscreens, and temperature variations, and you get a tired gasket after a few seasons. Water resistance is not a characteristic set in stone: it's a state that needs to be maintained. Hence the importance of taking care of your timepiece rather than blindly trusting it.

*Torus: A surface of revolution generated by a circle rotating around an axis located in its plane and not passing through its center.

ATM, Bars, or Meters?

These three indications refer to units of pressure whose values are almost equivalent (1 ATM = 1.01325 bar). For clarity, we will assume that 1 ATM = 1 bar = 10 meters of pressure.

Let's add that the values associated with these units are the result of laboratory tests and not real-world use, and require the following clarifications (to be learned by heart).

Translation: the 100 meters displayed on your dial are not an invitation to descend to 100 meters. This is 10 bars applied to a stationary watch, in a tank, at a stable temperature. However, an arm cutting through water during a crawl generates pressure spikes far greater than the actual depth. The watchmakers' rule of thumb: divide by two, and you'll be safe.

Note that Kelton also offers 20, 30, and 40 ATM models in its 1955 collection. If there is no mention of ATM or equivalent, be cautious: keep your watch away from water!

What can I actually do with my watch?

Because a table is good, but real life rarely happens in a laboratory tank, here's the real-world version.

• Water resistant to 30 meters (3 ATM): you wash your hands, you get caught in the rain on the way to the office, you spill a drink. That's it. No showering, no swimming pool, no washing dishes. A splash-resistant watch, not a water watch.
• 50 meters (5 ATM): Surface swimming becomes possible. A few gentle laps, a swim by the beach. However, avoid diving and speed sports: impact multiplies instantaneous water pressure.
• 100 meters (10 ATM or ATM 100): The real turning point. Swimming, snorkeling, jumping off the dock, all surface water activities. This is the minimum threshold to never have to worry about it again.
• 200 meters (20 ATM) and beyond: Sport diving, freediving, and the right to see what's happening in deep waters. This is where the true dive watch begins, one that can withstand pressure without flinching.

 

ISO 6425 Standard

When it comes to scuba diving, people's safety is at stake, and this standard was put in place to ensure that your watch reliably accompanies you into the abyss. It's worth noting that while many of us love dive watches, diver's watches, all these ultra-robust and luminous timepieces, the proportion of divers represents only 0.07% of the world's population, which is small ;)

The ISO 6425 standard includes 12 criteria (to be consulted in full at https://montredeplongee.com/norme-iso-6425/)

This label is not awarded lightly: readability at 25 cm in complete darkness, graduated unidirectional bezel, resistance to magnetic fields and shocks, endurance against temperature variations and thermal shock, and especially a test at 125% of the nominal pressure—every single watch, not just a sample. A professional dive watch certified ISO 6425 is, therefore, literally a safety instrument disguised as a stylish accessory.

Our Kelton 1955, as well as some of our other models, meet many of these criteria, without, however, claiming professional use. All have a sapphire crystal, a unidirectional bezel (dive time), a screw-down crown, and Super-LumiNova-coated indices and hands, which already allows for countless sports and water activities, from beach tennis to surfing, washing dishes, or even a mega cannonball in the Bay of Villefranche-sur-mer.

Thermal shock, a subtle enemy

We often imagine the sworn enemy of water-resistant watches as a wave. The reality is more unexpected: it's thermal shock. A sauna followed by an icy plunge, a scorching hot watch on the sand then a direct dip in the Mediterranean, a boiling shower after a sea bath: each time, metal and gaskets expand and then contract at different rates. The result is a micro-gap opening, the air inside the case contracts, and sucks in moisture. Fog under the crystal is almost never a waterproofing defect—it's a poorly managed temperature variation. Moral of the story: let your timepiece acclimate before subjecting it to extremes.

How to preserve your watch's water resistance?

Here, common sense is king, and simple rinsing after a sea swim or pool dip (in the shower) is recommended. Likewise, do not unscrew the crown underwater, not even for fun.

A few extra habits:

• Always check that the crown is securely screwed down before putting a toe in the water. 90% of damage comes from this.
• Rinse with clean, lukewarm water after the sea or chlorine, then dry with a soft cloth. Salt crystallizes and attacks the gaskets.
• Avoid directing a strong stream from the tap when you wash your hands: a pressurized stream of water creates more stress than a meter of depth.
• Have the water resistance checked approximately every two years, and systematically after the case back has been opened.
• Leather strap + seawater: no. Opt for FKM or steel for water activities.

 

Two questions we get all the time

Can a 50-meter watch go in the pool? Yes, for surface swimming. No for diving from the block or for the 250-meter slide.

Can I shower with my watch? Technically, from 10 ATM, yes. In reality, shower gel and hot water wear out the gaskets faster than the sea. Avoid it.

Is water resistance permanent?

No. It degrades over time, with shocks, and every time the case back is opened. It's a service, not a lifetime guarantee.

Warning: always consult a professional when you want to check a watch's water resistance, after any battery change or intervention on the case.
 

This article has been reviewed and validated by the Kelton technical team.