Water Resistance Ratings Explained

A water resistance marking is a laboratory result, not a promise about how deep you can go. Two separate standards govern the field: ISO 22810 for ordinary water-resistant watches, and the stricter ISO 6425 for diver's watches. Knowing which one applies changes how you read the number.

The standard behind an ordinary rating

The governing standard for ordinary water-resistant watches is ISO 22810:2010. This first edition cancels and replaces ISO 2281:1990, which it technically revised. ISO 22810 covers all watches, not only those made for water sport. Its predecessor ISO 2281 addressed watches for ordinary daily use, including short periods under water, and it explicitly did not apply to diver's watches, which are handled by ISO 6425 instead.

One consequence of the standard's language matters to collectors reading old and new marketing copy alike: the term waterproof is not permitted. It has been removed from professional watchmaking standards, and under ISO 22810 no manufacturer is allowed to use it. If you see it, you are reading loose language, not a certified claim.

What the tests actually do

ISO 22810 defines a static overpressure test in its own text. The pressure in the container is raised over one minute to a minimum overpressure of 2 bar, held there for 10 minutes, then reduced over one minute. Higher overpressure values can be specified by the manufacturer and marked on the watch, which is where larger figures on the dial or caseback originate.

The standard also prescribes shallow-immersion and crown-force checks. The watch is immersed in water to a depth of 10 cm plus or minus 2 cm and kept there for a minimum of one hour. In a separate step it is immersed to the same 10 cm depth for 5 minutes while a force of 5 N is applied to the crown and push-pieces perpendicular to their axis. That last test is the reason a screw-down crown left unscrewed can defeat an otherwise sound case.

Why a depth figure is not a usage depth

The single most misread element of any rating is the depth marking. A depth rating represents laboratory test pressure, not the depth at which a watch can be safely or repeatedly used. A watch marked 30 m is therefore not suitable for swimming or diving, because real movement, temperature swings, and aging gaskets impose loads the static bench test never simulates. Treat the number as a sealing benchmark measured once, on a new watch, under controlled conditions.

That gap between bench and pool is also why water resistance is a maintenance question, not a permanent property. Seals compress and dry out, and only a pressure test after service confirms the marking still holds. Manufacturer service guidance varies, and our journal covers what makers publish on the subject.

ISO 6425: the diver's standard

Diver's watches answer to a separate, stricter standard. Per ISO, ISO 6425 applies to divers' watches designed to withstand diving in water at depths of at least 100 m and equipped with a secured measuring system to indicate diving time that is visible in darkness. That 100 m floor is a hard requirement, not a marketing choice. The current edition listed by ISO is ISO 6425:2018.

The overpressure regime is more demanding than ISO 22810's. Reported test details put it at 125 percent of the watch's stated rating — for example a pressure equivalent to 250 m for a 200 m watch — held for 2 hours, after which the pressure is reduced to 0.3 bar, roughly 30 m equivalent, and held for a further hour. The 125 percent overpressure figure is corroborated across independent references.

Immersion is longer, too. The watch is immersed at approximately 30 cm for 24 hours, its functions are operated, and it remains immersed for another 24 hours, giving total exposure of about 48 hours with no water intrusion permitted. A thermal-shock check moves the watch between water pre-heated to 40 °C and cooled to 5 °C, with each transition taking less than one minute, cycling hot to cold to hot.

Non-water criteria

ISO 6425 also tests properties unrelated to depth. Reported requirements include rating within tolerance after exposure to a 4,800 A/m magnetic field, surviving a 5,000 g impact in two axes, and enduring 24 hours of salt-water immersion without function loss. The bezel must rotate only counter-clockwise, carry a minimum of 60 graduations, and hold position under accidental contact. Legibility is specified as well: time and bezel readable at 25 cm in total darkness for 60 minutes after a 5-minute light charge. These figures come from a single secondary source; only the 100 m floor is confirmed by ISO directly, so treat the rest as informed reporting.

Reading the DIVER'S marking

There is a shorthand on the dial itself. When a watch carries the marking DIVER'S together with a depth rating, the brand has formally certified it against ISO 6425. A plain water resistance figure with no such marking signals ISO 22810 territory instead, and should be read as a sealing benchmark rather than a diving credential.

How to use the two numbers

Read any bare depth figure as an ISO 22810 bench result: a controlled snapshot of sealing on a new case, not a license to submerge. Read a DIVER's marking with a depth as an ISO 6425 certification, backed by the longer immersion, thermal-shock, magnetic, shock, and legibility criteria above. In both cases the marking describes the watch on the test day, not after years of wear.

Water resistance sits alongside the other case specifications a buyer should verify before trusting a listing. For related reference material, see our blog, and if a specific caseback marking or claim needs a second opinion you can reach us through the contact page.

This page is informational. Figures and rules cited are accurate as of the review date above and can change.

Last reviewed July 30, 2026.