How is the water resistance of a watch measured?

When buying a watch, there is one criterion that must be taken into account: resistance to water pressure , more commonly called " waterproofness ". This is essential information to know if you can put your watch in contact with water and, above all, at what level of pressure. As you know, in watchmaking nothing is so simple, so there are a few subtleties to take into account. Rest assured, you should understand quickly, GUSTAVE & cie is here to make you a real expert in the field.

Understanding the water resistance of a watch

In watchmaking, a watch’s water resistance is measured in ATM (short for Atmosphere). This is the most widely used unit of measurement, although some brands use metres (m) or feet (ft). ATM measures the level of pressure that a watch and its movement can withstand. More specifically, 1 ATM is equivalent to 1 bar, or 10 metres of pressure. It also corresponds to the atmospheric pressure at sea level. As you may have guessed, a watch rated at only 1 ATM should not be considered suitable for contact with water. Likewise, if your watch does not display any water-resistance rating, it is best to keep it away from any source of moisture.

In the watch industry, the first commonly encountered level of water resistance is 3 ATM (30 metres). But does this mean that if you dive deeper than 30 metres your watch will stop working? Not at all. ATM ratings measure pressure under laboratory test conditions rather than a real-life depth of use. As a reminder, ATM ratings indicate the amount of pressure your watch can withstand. In reality, a few drops of water or sudden movements can already generate a level of pressure higher than you might imagine.

From 3 ATM to 20 ATM, there are several levels of water resistance corresponding to different uses. To understand whether your watch is simply resistant to splashes or suitable for more demanding aquatic activities, let us take a closer look at the different levels of water resistance..

The different sealing levels

These water-resistance ratings indicate the conditions under which your watch can come into contact with water and the activities that can be practised while wearing it. Below is an overview of the different levels you may encounter when purchasing a watch.

Waterproof watch 3 ATM (30 meters)

As mentioned above, this is the lowest rating commonly found and therefore the most restrictive when it comes to water exposure. A 3 ATM watch is not designed to withstand immersion. This level of water resistance protects only against occasional splashes, such as hand washing or rain.

5 ATM (50 meters) waterproof watch

A watch rated at 5 ATM offers a little more protection against water, but it is still important to take care of the movement. It will easily withstand everyday water exposure, such as hand washing or rain. However, we would stress that a 5 ATM watch is not designed for regular swimming or water sports. The pressure generated by a strong jet of water or certain movements in the water can place significant stress on the watch, so caution is advised. When customers purchase a watch in our boutique, we recommend viewing a 5 ATM watch as water resistant, but not as a true swimming watch. If you occasionally forget to remove it before brief contact with water, this should not cause any issues. Nevertheless, prolonged immersion is not recommended.

Waterproof watch 10 ATM (100 meters)

A watch with this level of water resistance can handle almost all forms of water exposure. It is perfectly suitable for swimming, lap swimming, occasional diving and even snorkelling. However, deeper underwater activities such as scuba diving are not recommended.

Waterproof watch 20 ATM (200 meters)

From this level onwards, you can enjoy your watch around water with complete peace of mind. Your timepiece is capable of withstanding most aquatic activities, including scuba diving. Once a watch reaches this level of water resistance, it is generally considered a true "diving" watch. There is no need to worry: it is designed for use in water and for water sports such as surfing or jet skiing.

Are there higher levels?

Indeed, if we ask the question, it is because there are watches that are even more waterproof than 20 ATM. For sports watches or watches designed specifically for professional diving, we can find a level of waterproofing of up to 200 ATM (yes, this corresponds to 2,000 meters).

Caring for a waterproof watch

Using your watch according to its level of waterproofness is necessary to keep it functional. However, there is one criterion that you must pay attention to in order to take even more care of it: condensation . This phenomenon results in fogging inside your glass or even small droplets. To avoid this, it is recommended to check that the crown used to wind the movement is properly screwed in before going into the water. This type of crown, specific to waterproof watches, prevents water from entering the mechanism. If ever a drop manages to find its way into your watch, it can create condensation, or even worse, seriously damage the movement.

Also, it is recommended not to subject your timepiece to thermal shock . Exposing your watch to the sun or high temperatures and then bathing with it in cold water may be one of the reasons causing condensation.

In any case, rest assured, condensation inside a watch is neither a rare nor serious phenomenon. To solve the problem, it is generally enough to leave your watch dry and in a rather warm place, letting the condensation evaporate. However, if this phenomenon is recurrent, it is advisable to go to your watchmaker.

After swimming in the sea, it is also recommended to rinse your watch under fresh water. This will remove any salt and sand deposits that may have remained on the glass or case, thus avoiding any risk of micro-scratches.

Finally, be aware that a watch is a fragile object and that its water resistance can be depleted over time. Every 3-4 years depending on the model, we recommend having your timepiece serviced by watchmaking professionals.

Conclusion

Finally, the most important thing is to keep in mind the future use of your watch to choose one that is more or less waterproof. The water resistance of a watch should no longer hold any secrets for you, so take the plunge and visit your watchmaker!