Water resistance is an essential feature of a watch, especially for sports, diving, or luxury models. It indicates the watch's resistance to water and moisture penetration.
But be careful: many people misinterpret the information on the dial or case back. Let's take a closer look.
What is water resistance in watchmaking?
Water resistance is the ability of a watch to withstand water pressure without water penetrating the case.
This protection depends on:
- case-back joint
- crown joint
- glass joint
- and sometimes the overall construction of the case.
Seals are never permanent: they age over time, due to heat, impact, or manipulation of the crown.
That is why regular checks are recommended (approximately every 2 years).
The main classifications of water resistance
Watches generally display their water resistance in one of the following units:
- meters (m),
- atmospheres (ATM),
-
or bars.
1 ATM = 1 bar = pressure equivalent to a depth of 10 meters underwater.
1. Non-waterproof watch (or “splash-proof”)
- Marking: “Water resistant 30 m” or “3 ATM”.
- Usage: hand washing, light rain, ambient humidity.
- No bathing, showering, or swimming.
Exemple : montres habillées, vintages, montres de ville, Obelus Simplissime.
2. Standard water resistance
- Marking: “50 m” or “5 ATM”.
- Usage: resistant to showers (without hot water) and light swimming.
- Avoid diving or jumping into the water.
Exemple : montres de sport polyvalentes, Obelus Chronoscope
3. Reinforced water resistance
- Marking: “100 m” or “10 ATM”.
- Use: swimming, snorkeling, light water sports.
- The perfect compromise for an everyday watch that can withstand anything.
Exemple : Obelus Boussole
4. Diving watches
- Markings: “200 m,” “300 m,” or more.
- Use: scuba diving, prolonged immersion.
-
Must comply with ISO 6425, guaranteeing:
- a unidirectional bezel,
- underwater readability,
- impact and salt resistance,
- and sometimes a helium valve (for saturation diving).
Exemple : Rolex Submariner, Omega Seamaster, Obelus Hydromatic.
5. Extreme water resistance
- Markings: “1000 m,” “3000 m,” or more (e.g., professional watches).
-
Designed to withstand very high pressures, often equipped with:
- ultra-thick cases,
- helium valves,
- and a reinforced screw-on base.
Example : Rolex Deepsea, Omega Planet Ocean Ultra Deep.
Key points to remember
| Misinterpretation | Ce que ça signifie vraiment |
| “30 m” does not mean that you can dive to 30 m. | This corresponds to a static pressure of 3 bar in the laboratory. |
| Hot water (bath, sauna, shower) destroys the seals. | Heat expands materials → water infiltration. |
| Salt and chlorine damage seals. | Always rinse the watch with fresh water afterwards. |
| The joints are aging. | Water resistance check every 2 years (at a watchmaker). |
In summary
| Water resistance | Indication | Recommended activities |
| 30 m / 3 ATM | Splashes | Hand washing, rain |
| 50 m / 5 ATM | Light use | Cold shower, quick bath |
| 100 m / 10 ATM | Multiple-use | Swimming, snorkeling |
| 200-300 m / 20-30 ATM | Diving | Scuba diving, water sports |
| 1000 m et + | Professional | Deep diving, saturation |