Watch tool
Water resistance checker
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On this page (6 sections)
Why the meter marking is not a depth
A watch marked 30 m cannot be taken 30 meters underwater. The figure comes from holding the case at a static pressure equal to that depth of water, at room temperature, on a watch that has just been made. Real water is dynamic: pushing your arm through a pool briefly raises the pressure at the crystal well above what the depth alone suggests, and a dive off a board spikes it higher again.
The standard behind ordinary water resistant watches is ISO 22810. It sets the tests and the marking rules, but it lets the manufacturer choose the rating and allows sample testing rather than testing every watch. The separate divers' standard, ISO 6425, requires every single watch to be tested and adds legibility, bezel and magnetic requirements. A high meter number alone is not the same claim as a DIVER'S marking.
| Question asked | ISO 22810 | ISO 6425 |
|---|---|---|
| How many watches are tested | A sample of the run is normal | Every individual watch |
| Minimum rating | None. Any figure may be marked | 100 m |
| Salt water, shock, magnetism | Not covered | All three required |
| Reading it underwater | Not covered | Legible in darkness, protected elapsed-time bezel |
| Marking earned | WATER RESISTANT and a figure | DIVER'S WATCH and a depth |
The exact durations, forces and temperatures belong in the standards documents; quoting them second hand is how false precision spreads. What matters is the shape of the two claims. Our guides to water resistance and to dive watches and ISO 6425 take each apart.
How to answer the three questions honestly
Each input has a common way of going wrong.
- The marked rating. Read it from the dial or the caseback, not from the product page of a similar reference. "WATER RESISTANT" with no figure is the basic marking and belongs in the 30 m column. 5 BAR and 5 ATM both mean 50 m.
- The crown. A screw-down crown must be unscrewed before it will pull out, and threads back with two or three turns of resistance. If it pulls straight out it is push-in, whatever a listing says.
- Seals and testing. The question is when the case was last pressure tested, not when it was last opened. A battery change with a fresh gasket proves nothing without a test afterward: choose "history unknown".
What the adjustments here are doing
Two things degrade a rating faster than depth ever will. The first is the crown. A screw-down crown clamps its gasket mechanically, which is why it is what makes a 200 m rating trustworthy, and an unscrewed crown makes any rating meaningless at that moment. The second is age. Gaskets are elastomers that take a compression set, harden with heat and get chewed up by soap, sunscreen and chlorine. A watch that has never been pressure tested has an unknown rating regardless of what is printed on the dial.
Mechanically, the tool moves each activity down one step for unproven seals, and one more step for a push-in crown claiming 200 m or 300 m, which is an unusual combination worth checking. Rain and splashes are never downgraded, because a case that fails at that level is already leaking. Note what it does not do: a screw-down crown never promotes a rating. A 50 m watch with a screw-down crown is still a 50 m watch, because the maker already had that crown in mind when it chose the number.
A worked example: two watches, one pool
Compare a 100 m watch pressure tested this year against a 200 m diver that has not been tested in years. The higher number loses.
| Activity | 100 m, tested this year | 200 m, not tested in years |
|---|---|---|
| Rain and hand washing | Yes | Yes |
| Showering | Only with care | No |
| Swimming in a pool | Yes | Only with care |
| Snorkeling | Yes | Only with care |
| Scuba diving | No | No |
Unproven seals cost one step on everything except rain and splashes, so the 200 m watch drops from a confident yes to a qualified one and its scuba answer falls away. The decision that follows is not "buy a better watch". It is to spend roughly $25 to $60 on a bench pressure test, indicative US pricing before sales tax, then re-run the tool. If it passes, the 200 m watch is the better swimming watch again. If it fails, you learned that for the price of a strap rather than the price of a movement.
The rules that no rating covers
No consumer water resistance rating covers hot water, steam rooms or saunas. Heat is a different failure mode from pressure: warm gaskets expand and contract, and a warm case plunged into cold water pulls a slight vacuum that draws moisture past a marginal seal. That is the classic way to fog a crystal on an otherwise healthy watch. Rinse in fresh water after salt or chlorine, never operate a crown or pusher while the watch is submerged, and have the seals tested about once a year if the watch goes in water at all.
Some things the tool cannot see at all. A vintage watch has a rating that expired decades ago, and an acrylic crystal and pressed caseback that were never meant for modern swimming. A chronograph adds two more openings in the case, and unless its pushers screw down they should be treated as the weak point. A leather strap will suffer in water long before the case does. And a crown that has been cross-threaded, or a caseback closed without seating its gasket, can fail at zero depth: if yours will not screw down cleanly, stop and have it looked at.
What to do with the answer
- Book a pressure test if the tool downgraded you for seals, and ask for the result in writing. Budget $25 to $60 alone, or roughly $40 to $80 bundled with a battery change, before sales tax.
- Change the behavior, not the watch, if the rating is simply low. No amount of care makes a 30 m case into a swimming case.
- Buy for the wettest thing you actually do. If that is scuba, buy a watch marked DIVER'S under ISO 6425 rather than a 300 m watch that looks the part. Our guide to servicing and care covers the upkeep either choice implies.
Common follow-up questions
Is 50 m water resistance enough for swimming?
It is the gray zone. 50 m survives accidental immersion and brief, gentle, shallow swimming on a watch whose seals have been tested recently. For regular swimming, 100 m is the first rating that is genuinely comfortable, which is why the tool answers "only with care" at 50 m and "yes" at 100 m. There is more in our answer on swimming with a 50 m watch.
How often should the seals be tested?
About once a year if the watch goes near water, and any time the case has been opened for a battery, a service or a bracelet change. A bench pressure test typically runs roughly $25 to $60 in the US, before sales tax, depending on the shop and the market.
Does this tool know my specific watch?
No, and neither does any tool. It applies the general relationship between rating, crown type and seal condition. Your owner's manual and a pressure test at a watchmaker are the only sources that describe your watch.
Can I shower with a 100 m watch?
The tool says "only with care", and the caveat is heat rather than pressure. Hot water softens gaskets and drives the expansion and contraction cycle that pulls moisture in, and shower gel and shampoo attack rubber. A watch that showers daily needs its seals tested more often, not less. See showering with a watch.
Why does a screw-down crown not improve the rating here?
Because the manufacturer already accounted for it. The rating is a property of the whole sealed case, crown included, so a screw-down crown is part of the reason a 200 m watch earns 200 m rather than a bonus on top. What the tool does do is flag the reverse case: a push-in crown on a 200 m or 300 m claim is unusual and worth checking against the specification.
Do I need a helium escape valve?
Almost certainly not. That valve exists to vent helium that works its way into a case during days spent in a saturation diving chamber, which is commercial and military work. It does nothing for recreational diving, swimming or anything on land.
Sources and further reading
- ISO 22810, Horology: Water-resistant watches. The standard governing the words "water resistant", the pressure markings on ordinary watches, and the fact that the manufacturer chooses the rating and may test a sample rather than every watch.
- ISO 6425, Horology: Divers' watches. The source of the DIVER'S marking, the 100 m minimum, the salt water, shock and magnetism requirements, the legibility requirements and the rule that every individual watch is tested.
- Owner's manuals published by makers such as Seiko, Citizen and Omega, which set out crown handling, rinsing after salt water and the recommended interval between pressure tests for a specific watch.
- Indicative US bench pricing for pressure testing and for a battery change with a gasket and test, quoted before sales tax. Bench rates differ between workshops and markets and move over time.
Last reviewed 4 September 2026. Spotted an error? Tell us and we will fix it in public.