Watch Water Resistance Explained: What 10 ATM and 30 ATM Really Mean

There is probably no specification on a watch more misunderstood than water resistance.

Most people assume a 30-metre rating means the watch survives 30 metres underwater. Others think any watch with a water resistance rating can be worn in the sea. And plenty of watch owners have learned the hard way that "splash resistant" and "waterproof" are not the same thing.

In this guide, we break down exactly what water resistance ratings mean, why the numbers on paper are different from real-world performance, and what the difference is between a 10 ATM everyday watch and a 30 ATM dive watch. We use the Soren Momentis and Oceanic as real-world examples — because they sit at exactly these two ratings.

What Does ATM Mean on a Watch?

ATM stands for "atmospheres" — a unit of pressure. One atmosphere (1 ATM) is equal to the air pressure at sea level. In water, pressure increases by roughly 1 ATM for every 10 metres of depth.

So when a watch is rated to 10 ATM, it means the case and crown have been tested to withstand a static water pressure equivalent to 100 metres depth. A 30 ATM rating equals 300 metres.

Simple enough. But here is where it gets complicated.

The Static vs Dynamic Problem

Water resistance ratings are determined in a laboratory under controlled, static conditions. The watch is submerged in still water or pressurised in a testing chamber. Real life is nothing like that.

When you swim, the movement of your arm creates dynamic pressure against the watch that significantly exceeds static depth pressure. Jumping into water creates a sudden impact that can generate pressures far beyond what the rating suggests. A 3 ATM watch rated to 30 metres can fail from the impact of a cannonball dive into a pool.

Temperature also plays a role. Switching from a hot shower to cold water causes metal and seals to expand and contract. Over time, this degrades the rubber gaskets that keep water out. Even a well-sealed watch loses water resistance as seals age.

This is why the practical guidelines for water resistance are far more conservative than the rated depths.

The Complete Water Resistance Rating Guide

1 ATM / 10m Splash resistant only. Light rain is fine. Not suitable for any water activities.

3 ATM / 30m Rain and accidental splashes are fine. No swimming, no showering. Common on dress watches and fashion watches.

5 ATM / 50m Suitable for showering and light swimming in still water. No diving. Bare minimum for daily wear.

10 ATM / 100m The sweet spot for most people. Suitable for swimming, snorkelling, and recreational water sports. Not for scuba diving. This is where the Soren Momentis sits.

20 ATM / 200m Suitable for recreational scuba diving. Watches at this level typically feature screw-down crowns and reinforced cases.

30 ATM / 300m Professional dive watch territory. Built and tested to ISO 6425 — the international standard for diver's watches. This is the rating of the Soren Oceanic.

Beyond 30 ATM Saturation diving watches used by professional deep-sea divers. Highly specialised instruments for commercial and military diving.

What Is ISO 6425?

ISO 6425 is the international standard that defines what a true diver's watch must be capable of. It is far more demanding than a simple depth rating.

To be certified under ISO 6425, a watch must pass:

• Water resistance to 125% of its rated depth
• Resistance to shock from a 3kg impact
• Resistance to magnetic fields
• A clearly legible display underwater, including luminous markers visible after darkness adaptation
• A unidirectional rotating bezel that cannot accidentally extend a diver's bottom time
• A minimum power reserve of one hour before the watch stops

Not every watch rated to 30 ATM meets ISO 6425. The ISO certification is earned, not assumed. The Oceanic is built to these standards — with a unidirectional bezel, screw-down crown, and luminous markers designed for low-visibility conditions underwater.

10 ATM in the Real World: The Soren Momentis

The Soren Momentis is rated to 10 ATM — 100 metres.

In practice, that means you never need to think about water with this watch. Morning shower, afternoon swim, evening drinks by the harbour — it handles all of it without concern. The 10 ATM rating puts it firmly in the category of serious sports watches, well above the splash-resistant lifestyle watches that dominate the sub-€500 market.

The Momentis is a 40mm Swiss Made automatic powered by the Sellita SW200-1 — one of the most reliable automatic movements produced today. Its 316L stainless steel case is sealed to 10 ATM with a solid caseback, and the sapphire crystal adds scratch resistance that cheaper mineral glass cannot match.

For the vast majority of people — whether you swim a few times a week, travel regularly, or just want the confidence that your watch handles whatever your day throws at it — 10 ATM is the right rating. It covers everything short of scuba diving.

The Momentis is available in five dial colours on both Jubilee and Oyster bracelets, starting from €625.

30 ATM in the Real World: The Soren Oceanic

The Soren Oceanic is rated to 30 ATM — 300 metres.

This is not a casual upgrade from 10 ATM. It represents a fundamentally different construction approach. The Oceanic is built as a tool watch first — every detail serves a function.

The unidirectional rotating bezel exists for one reason: to track elapsed dive time safely. It only rotates one way so that if it gets knocked accidentally underwater, your dive time is extended rather than shortened — the safer error. The screw-down crown creates a mechanical seal that stands up to serious water pressure. The luminous markers are applied to be visible after your eyes have fully adjusted to darkness, 20 metres below the surface.

The Oceanic is also powered by the Sellita SW200-1, in a 40mm 316L stainless steel case. Swiss Made certified. At 30 ATM, it is rated for recreational scuba diving and built to the same standard as dive watches costing significantly more.

The Oceanic is available in Black, Blue, Green, All Blue, and All Green on both Oyster and Jubilee bracelets, starting from €695.

How to Maintain Water Resistance

A watch's water resistance is not permanent. Here is how to protect it:

Rinse after salt water. Salt is corrosive. After any ocean exposure, rinse your watch in fresh water and dry it with a soft cloth.

Avoid temperature shocks. Hot tubs and saunas are not recommended for any watch — heat combined with chemicals degrades rubber gaskets faster than cold water alone.

Service the seals every 2 to 3 years. If you regularly expose your watch to water, have the water resistance re-tested and seals replaced as part of routine servicing.

Never operate the crown underwater. The crown is the most vulnerable point on any case. Even a screw-down crown should never be adjusted while submerged.

Check the crown before water exposure. Make sure it is fully pushed in — or screwed down on the Oceanic — before any swimming or diving.

Common Water Resistance Myths

"My watch is waterproof." No watch is waterproof. They are water resistant to a rated level under controlled conditions. Even deep-rated dive watches can fail if seals are degraded or crowns are open.

"It survived last time, so it will be fine." Seals degrade over time. A watch that handled a dive three years ago may not handle the same dive today.

"30 ATM means I can dive to 300 metres." The 300-metre rating exists to ensure reliable performance at the depths recreational divers actually use — typically under 40 metres. The headroom is the point.

"Higher ATM is always better." For most people, no. A 10 ATM watch like the Momentis is more than adequate for daily life and swimming. Choose based on your activities, not the number.

10 ATM or 30 ATM: Which Is Right for You?

Choose the Momentis if you want a versatile everyday automatic that handles swimming and travel without a second thought, and looks as good with a suit as with a t-shirt.

Choose the Oceanic if you dive, surf, or spend serious time in the water. Or if you want a purpose-built tool watch with the confidence of a 300-metre rating and a bold diver's aesthetic to match.

Both watches are Swiss Made. Both run on the Sellita SW200-1. Both are 316L stainless steel with sapphire crystal. The difference is one of intent — a refined everyday automatic versus a purpose-built dive watch.

Either way, you are getting a Swiss Made automatic for under €700.

Shop the Soren Momentis — Swiss Made Automatic, 10 ATM, from €625 https://sorenwatches.com/collections/momentis

Shop the Soren Oceanic — Swiss Made Dive Watch, 30 ATM, from €695 https://sorenwatches.com/collections/oceanic

Related: Oyster vs Jubilee Bracelet: Which Should You Choose?