Watch Water Resistance and ATM Ratings – A Comprehensive Guide and Testing
This guide has been produced by Kulta-Aika's team of experts. With decades of experience in the watch industry and the support of our skilled watchmakers, we offer you the most reliable information on watch maintenance and features.
Did you know? The deepest diving wristwatch in the world has reached a depth of almost 11 kilometers in the Mariana Trench and returned to the surface completely unharmed. In everyday life, however, the biggest threat to your watch's water resistance is not the depth of the ocean – but an ordinary Finnish sauna.
Is a watch water resistance test current? A watch's water resistance is not a permanent feature, as over time the watch's gaskets dry out, become brittle, and lose their flexibility. It is therefore advisable to have your wristwatch's water resistance checked regularly every 3–5 years, or even annually if the watch is actively used for swimming or diving. The water resistance test can be most conveniently performed in conjunction with a watch battery change.
Watch water resistance test cost and service process
The cost of testing a watch's water resistance alone is about 20 euros. The test measures with a device how much pressure the watch case can withstand. If necessary, our watchmaker will replace the watch's case back gasket or crown gaskets if the device detects leaks or if the gaskets show clear signs of wear.
The most convenient and affordable option is to perform the water resistance test at the same time as a battery change, with a total cost of approximately 30 euros. Since the watch is opened during a battery change, the original water resistance marking on its case back is no longer valid as such. Pressure testing is particularly important if your watch's water resistance rating is at least 10 ATM (100 m), meaning it is intended for swimming or diving.
Our watchmakers pick up watches from our stores and service them in their own workshop. Your watch is typically available for pickup from your chosen store within 3–5 business days. If you wish, we can also deliver your watch directly to the official service center of the importer (for example, Swatch Group or Watch Service Finland). In this case, we will provide a separate price estimate, and the service duration will be approximately 3–5 weeks, depending on the importer.
Bring your watch to an expert
We serve you flexibly without an appointment in our stores:
- Watch water resistance test Helsinki – Kulta-Aika Kamppi, Kamppi Shopping Center
- Watch water resistance test Vantaa – Kulta-Aika Tammisto, Säätökuja 2B
We also offer comprehensive watchmaker services, with a free repair estimate if desired!
What do watch water resistance markings really mean?
Watch water resistance is indicated by several different markings, such as meters (m), atmospheric pressure (ATM), and bar (bar). These all mean essentially the same thing: 30 m = 3 ATM = 3 bar. However, it is extremely important to understand that the meter reading does not indicate the permitted diving depth.
When a watch undergoes a water resistance test at the factory, it occurs in completely static laboratory conditions. In real life – for example, when swimming – the movement of the hand in water creates dynamic pressure on the watch, which is significantly greater than the static pressure of stationary water. Therefore, a "30-meter" (3 ATM) water-resistant watch can actually only withstand light splashes, not diving to a depth of 30 meters. If there is no water resistance marking on the watch's case back, it should be carefully protected from all water and moisture.
Water resistance classes and their uses
| Marking (ATM/m/bar) | Practical meaning | What does the watch withstand? |
|---|---|---|
| 3 ATM / 30 m | Splash-resistant | Withstands occasional splashes (rain, hand washing). Should not be exposed to running water or submerged. |
| 5 ATM / 50 m | Limited water resistance | Withstands quick wetting. However, swimming or showering is not recommended. |
| 10 ATM / 100 m | Water-resistant | Suitable for surface swimming, snorkeling, and showering. Not suitable for scuba diving. |
| 20 ATM / 200 m | Highly water-resistant | Suitable for scuba diving, water sports, and heavy use in water. |
| 30 ATM / 300 m+ | Professional use | Designed for professional scuba diving, often equipped with a helium valve. |
Many high-quality Swiss watch manufacturers already set 10 ATM (100 m) water resistance as a basic standard for their everyday watches. For example, all sporty Certina watches and many popular Candino watches are built to at least this class, making them perfectly capable companions for Finland's varying weather conditions and swimming trips.
Explore the wristwatch selectionOfficial water resistance tests: ISO 2281 and ISO 6425
In addition to mere ATM markings, some watches receive official international classification. The most common of these are ISO 2281 for everyday watches and the highly demanding ISO 6425 for diver's watches.
Everyday watch classification (ISO 2281)
To receive this marking, no condensation must accumulate inside the watch during testing. The watch is subjected to, among other things, a pressure test (at least 2 bar), a separate water droplet test (measuring the effect of thermal shock on the crystal), and immersion tests alternately in 40 °C and 20 °C water. The watch reliably withstands moisture, but is not a true diver's watch.
Diver's watch classification (ISO 6425)
This classification requires extreme durability from watches, and it often increases the price of the watch due to lengthy testing processes. A diver's watch is required to have, among other things:
- Resistance to prolonged saltwater immersion without corrosion.
- Guaranteed readability in complete darkness from at least 25 centimeters.
- Tolerance to magnetic fields and strong impacts.
- Exceptional tensile strength of the bracelet and spring bars.
The most incredible water resistance records in watch history
The first water-resistant watch and the English Channel: The revolution in watch water resistance began in 1926 when the world's first completely water and dust-resistant wristwatch was introduced. The very next year, young British swimmer Mercedes Gleitze swam across the English Channel with the watch around her neck. After ten hours of chilling swimming, the watch was still working perfectly, and the era of water-resistant watches had officially begun.
Journey to the deepest place in the world: The current world record for water resistance was set in 2019. A specially manufactured prototype watch was attached to the exterior of a submersible and lowered into the Mariana Trench to a depth of no less than 10,935 meters. The watch effortlessly withstood the crushing pressure of over a thousand atmospheres and still accurately told time on the surface.
Liquid-filled watches: How do you build a watch that can withstand essentially infinite pressure? The answer is liquid. Some of the most advanced special diver's watches on the market are completely filled with silicone oil. Because liquid cannot be compressed like air, these watches can withstand the pressure of any ocean floor. As a bonus feature, the oil completely eliminates reflections from the crystal underwater, making the watch face perfectly readable from any angle.
Everyday dangers: How to keep your watch water resistant
- Heat is the watch's worst enemy: No watch, not even a 300-meter diver's watch, should be taken into a sauna or hot tub! Heat expands the metal parts of the watch, and steam can penetrate the brittle gaskets into the movement. Sudden temperature shocks, such as going directly from the sauna to an ice hole, are also destructive.
- Chlorine, salt, and soap: If you have been swimming in seawater or a swimming pool, always rinse the watch thoroughly with fresh tap water. Chemicals and salt corrode rubber gaskets quickly.
- Using a screw-down crown: Diver's watches usually have a screw-down crown. Always ensure that the crown is screwed down firmly by hand before swimming. However, do not overtighten it with tools to avoid damaging the threads. Never use the watch's pushers (e.g., for chronograph functions) underwater unless specifically allowed by the manufacturer.
- Condensation vs. leakage: If the watch crystal fogs up temporarily on the inside, for example in freezing temperatures, it may be natural condensation. However, if the fog remains on the crystal for a long time or turns into water droplets, the watch is leaking and should be taken to a watchmaker immediately to prevent corrosion of the movement.
Frequently asked questions about watch water resistance
Can I shower with my watch on?
Showering is only recommended for watches with a water resistance of at least 10 ATM (100 m). It should also be noted that shampoos and warm water stress the watch's gaskets more than cold water alone.
What does "Water Resistant" mean?
A mere "Water Resistant" marking (without a meter reading) usually corresponds to a 3 ATM (30 m) rating. It means that the watch is only splash-resistant. It can withstand small everyday splashes, but it should not be submerged in water.
Is a smartwatch water-resistant?
Most modern smartwatches are at least splash-resistant, and sports watches often withstand swimming. However, with smartwatches, it is extremely important to check the manufacturer's own instructions (IP rating or ATM marking), as the device's speakers and microphones can be sensitive to water pressure.
My watch crystal is fogged up inside, what should I do?
Take the watch to a watchmaker immediately. Moisture inside the watch will very quickly start to corrode the metal parts. As a first aid, you can keep the watch in a dry and warm place (e.g., under a desk lamp, but not too hot), but professional drying and gasket replacement are essential.