Watch water resistance: the definitive guide to ATM, bar, metres

You've just bought a watch displaying "50M WR" on the dial and you're wondering if you can wear it to the swimming pool. Or perhaps your "10 ATM" watch has already taken on water during a sea dive. Watch water resistance is the most misunderstood subject in the mass-market watch industry: the figures engraved on cases are indices of static pressure in the laboratory, not guarantees of actual diving depth. This definitive guide, written by Frédéric Blanc (15 years in European watch trading), debunks received ideas with figures to back them up, explains ISO 22810 and ISO 6425 standards without unnecessary jargon, and gives you the reference table that forums have been sharing for years. Bookmark this page: you'll be back.

Also worth discovering: our water resistance barometer for the French watch market 2026 (exclusive study on 3,893 references, rankings by brand).

Watch water resistance: what the ATM, bar and metre markings really mean

When a watchmaker engraves "5 ATM" on a case back, they are indicating the static pressure to which the case was subjected in the laboratory during a water resistance test. The ATM (atmosphere) is a unit of pressure: 1 ATM equals 1.013 bar, or approximately the atmospheric pressure at sea level. By watchmaking convention, 1 ATM is considered to correspond to 10 metres of water column under perfect static conditions.

The bar is the SI unit closest to ATM (1 bar = 0.987 ATM), used interchangeably in technical datasheets. The marking "5 ATM", "5 bar" and "50 m" on three different watches therefore theoretically designates the same level of laboratory resistance. What changes radically is the standard applied during the test. To learn more about the exact correspondence between indices, consult our detailed guide on water resistance indices ATM, bar and metres.

The real problem: none of these indices is a promise of actual diving depth. The pressure exerted by a dynamic dive (entering the water from a platform, wave, pressure jet) can exceed the static test value by 3 to 5 bar. A case certified at 5 ATM in the laboratory can therefore be exposed to more than 7 bar during a simple dive in a swimming pool. This physical reality is documented in the ISO 22810:2010 standard itself, which explicitly distinguishes between test conditions and usage conditions.

Finally, watch water resistance degrades over time. Elastomer seals age, crack and lose their resilience. A "10 ATM" index on a watch purchased in 2019 without servicing since is very probably lower than its nominal value today. This point is systematically ignored in product datasheets, and it is one of the first subjects addressed during a professional watch service diagnosis.

The definitive watch water resistance table: ATM, bar, metres and real-world use

The table below summarises the correspondences between the engraved indices, the actual test pressures, and the safe uses according to ISO 22810:2010 and ISO 6425:2018 standards. The symbols ✓ (safe use), ⚠ (risky use, to be avoided), ✗ (prohibited use, water ingress likely) are aligned with the recommendations of the two standards and the technical guides of the FFESSM (French Federation of Underwater Studies and Sports).

Important technical note: the ISO 6425:2018 standard requires that the pressure resistance test be carried out at 125% of the declared nominal depth. A watch certified "Diver's 200 m" is therefore tested at 250 m of equivalent pressure, or 25 bar. It is this over-test that gives it its true reliability in dynamic diving, whereas a simple "200 m WR" ISO 22810 will only be tested at 20 bar static.

ISO 22810 and ISO 6425: the two standards every buyer should know

The ISO 22810:2010 standard (available on iso.org) defines the minimum requirements for a watch to bear the "Water Resistant" (WR) marking. It applies to virtually all watches on the consumer market: entry-level quartz, sports chronographs, dress watches with non-screw-down crowns. The test is static: the case is immersed in a sealed pressure chamber, without case movement or thermal shock. The standard also specifies that the test is of a "type" nature and may not be performed on each piece produced in series, unlike ISO 6425 requirements.

The ISO 6425:2018 standard (revised in 2018, formerly 1996) applies exclusively to diving watches. It imposes five cumulative protocols that ISO 22810 does not require: resistance to dynamic pressure (case in motion), resistance to thermal shock (alternating cold water 5°C / hot water 40°C), resistance to a magnetic field of 4,800 A/m, resistance to mechanical shocks (two shocks at 5,000 g), and dial readability at 25 cm in total darkness. The marking "DIVER'S WATCH X M" inscribed on the dial or case back is the only visual indicator of ISO 6425 compliance.

In practice: if your watch indicates "100 m WR" without the "DIVER'S" marking, it complies with ISO 22810 but is not certified for sports diving. Brands offering ISO 6425 watches are rare: notably Seiko Prospex Diver (SSC, SRP, SNE ranges), Citizen Promaster Diver, and Rolex Submariner and Sea-Dweller. These references represent approximately 5% of the global watch market. For anything concerning diving with certification, consult our dedicated guide: water-resistant 200 m watch for diving.

The myth of 50 m: why 5 ATM does not mean 50 metres of diving

This is the central counter-intuition of all water-resistant watchmaking, and it is absent from 90% of product datasheets online. When you dive into a swimming pool from the edge (dive from approximately 1 m height), the pressure exerted on the case is not that of a static water column. Fluid mechanics equations show that a dynamic impact at the water surface generates shock pressure that can reach 3 to 5 bar additional compared to hydrostatic pressure at the entry depth.

Concrete result: a watch worn at 1 m real depth after a standard dive can experience peak pressure of 6 to 8 bar, equivalent to 60 to 80 m of static pressure. A case certified 5 ATM (5 bar static) is therefore frequently exposed to pressures exceeding its nominal value during a simple pool dive. This is why the ISO 22810:2010 standard explicitly states in its annexes that 3 ATM and 5 ATM watches are not designed for voluntary immersion.

The practical rule adopted by professional watchmakers since the 1980s is as follows: divide the ATM rating by 2 to obtain an estimate of the safe real-world depth of use. That is: 5 ATM → approximately 2.5 ATM real usable repeatedly, 10 ATM → 5 ATM real, 20 ATM → 10 ATM real. For swimming in a pool without diving, this rule indicates that 10 ATM is the reasonable minimum threshold. Our full article on 5 ATM watches details precisely what you can and cannot do with such a rating in daily use.

Another aggravating factor often overlooked: pressurised water jets (standard pressure showerhead: 3 to 6 bar at the nozzle outlet) can locally exceed the nominal resistance of a 3 ATM case if the jet is directed straight at the crown or case back. The crown gasket is the weakest point most exposed in this configuration, as we detail in the next section.

What water resistance level for what actual activity

The question our customers ask most often before purchase: "can you swim with your watch?" The answer depends entirely on the rating, the standard applied and the type of activity. Here is the operational scale we apply in daily purchase advice.

3 ATM / 30 m: light splashes and rain only. Avoid high-pressure showers, swimming and any voluntary immersion. The majority of dress watches, fashion watches and vintage pieces without marking fall into this category or below.

5 ATM / 50 m: shower without direct pressure on the crown, surface swimming without diving. Not suitable for pool swimming with repeated dives or sea with waves. This is the most frequent threshold on "sport" city watches and Japanese entry-level models. Our guide 5 ATM: understand everything explores this threshold in detail.

10 ATM / 100 m : swimming pool, calm sea, surface snorkelling, water sports. This is the first truly versatile level for regular sports use. The vast majority of Casio G-Shock sports watches, Edifice chronographs and Citizen automatic sports models reach this threshold. Find our full analysis in the guide Casio 10 ATM: everything you need to know. Diesel large-diameter watches generally also reach this level, making them popular choices for summer marine use.

20 ATM / 200 m without DIVER'S : shallow snorkelling possible, but without guarantee for deep sports diving. Casio G-Shock models such as the GA-110SG-4AER reference reach this threshold: their mechanical robustness partially compensates for the lack of ISO 6425 certification, but for bottle diving, certification remains essential.

Diver's 200 m or 300 m ISO 6425 : bottle diving, sports diving, professional use. Only this level guarantees resistance to thermal shock (warm surface water / cold deep water), compass magnetic fields and dynamic pressure. Seiko Prospex, Citizen Promaster Diver and Rolex Submariner are the references in this segment. See our guide water-resistant watches 200 m for diving.

For selections tailored by gender, consult our guide water-resistant watch for men and our guide water-resistant watch for women, which detail the models available in clearance at each water-resistance level.

The 3 weak points that cause loss of water resistance (seals, crown, crystal)

A watch case is a system of three water-resistant barriers: the crown seal, the case back seal and the crystal seal (bezel or crystal). Each can fail independently, and a single failure is enough to flood the movement. Here are the three critical points to monitor.

Weak point no. 1: the crown seal. This is the leading cause of water ingress recorded in watchmaking workshops. The crown seal is an elastomer ring (usually nitrile or fluorocarbon) housed in the crown tube. Exposed to UV, sunscreen, chemicals (pool chlorine, seawater) and temperature variations, it weakens in 3 to 5 years depending on usage conditions. A crown not repositioned correctly after time adjustment (not screwed down on a screw-down crown model) is the no. 1 cause of water ingress reported in after-sales service. On screw-down crown models, the recommended tightening torque by manufacturers varies between 0.1 and 0.3 N/m depending on diameter: do not tighten "by hand" without a reference.

Weak point no. 2: the case back seal. Located between the case back and the case middle, this seal is generally nitrile (flexible, resistant up to 120°C) or a metal O-ring on high-end diving watches. Its lifespan is longer: 5 to 10 years in normal use. However, any screwing or unscrewing of the case back (battery change, movement inspection) without seal replacement immediately exposes the movement. A static pressure test at 3 bar in the workshop (approximately 15 to 20 €) verifies the integrity of this seal without disassembly.

Weak point no. 3: screw-down crown but simple pushers. Many "10 ATM" sports watches on the market are equipped with a screw-down crown (strong point) but non-sealed chronograph pushers (critical weak point). Operating a pusher underwater on this type of case creates a direct entry path for water. This defect is common on mid-range chronographs. To identify this point: check whether the pushers are clearly mentioned as "sealed" or "screwed" in the technical sheet. In the absence of this mention, never operate the pushers underwater. If you observe condensation after water exposure, consult our guide watch condensation: condensation or water-resistance problem to diagnose the situation.

The home water-resistance test: the warm water glass method

This simple test has been used for decades by professional watchmakers as a quick screening before formal overhaul. It is based on a physical principle: warm air expands and seeks to escape from the case, whilst warm water (denser than the air inside) penetrates if the seals are failing. The effect is amplified by the temperature difference between the air inside the case (ambient, 20-22°C) and the test water (35-40°C).

Step-by-step protocol:

1. Fill a large glass with water at 35-40°C (hot tap water, not boiling).
2. Check that the crown is closed and, if screw-down, properly screwed down.
3. Immerse the watch completely, case horizontal, dial facing up.
4. Wait 5 full minutes without touching the watch.
5. Remove the watch, dry it immediately with a clean cloth.
6. Observe the crystal and case back under raking light (desk lamp tilted at 30°) or under UV lamp if available.

Interpretation: any misting under the crystal, any visible droplet on the dial or inside the case signals active water ingress. If the test is negative (no misting, no condensation), the water resistance is functional for uses corresponding to the declared rating. This test does not validate compliance with the ISO standard: only a certified pressure test in a workshop does that. But it detects serious failures before a purchase, a service or use in an aquatic environment.

This test is particularly relevant in the context of buying an outlet or second-hand watch: clearance stock pieces are authentic and guaranteed, but a crown seal that has been in stock for 12 to 18 months deserves systematic verification before intensive aquatic use. If in doubt, our team is available via the contact page to guide you towards appropriate inspection procedures.

How much does a water resistance re-certification cost at the watchmaker in 2026

The price list below is based on rates charged by independent French watchmaking workshops in 2026, as documented in the Journal du Chrono and consolidated by our 15 years of experience in European watch trading. These prices are exclusive of a complete movement service.

Preventive seal service every 2 to 3 years is the standard recommendation from manufacturers for watches with regular aquatic use (Seiko and Citizen state this explicitly in their maintenance manuals for the Prospex and Promaster Diver ranges). Neglecting this is the main reason why new watches guaranteed "200 m" end up flooded after 4 years of use without servicing. On a premium-tier watch, the cost of a flooded movement consistently exceeds the cost of 5 preventive seal services.

For watch water resistance standards and certification levels, an authorised workshop can issue you a water resistance certificate after service: systematically demand this document if you are reselling a watch or if you engage in professional diving. It constitutes proof of value when transferring ownership.

Our selection: water-resistant watches available in clearance stock

Here are references available at outlet price on Montres Outlet, selected for their genuine water resistance level and their quality-to-ATM ratio. Each piece is authenticated and delivered with a 2-year the 2-year warranty.