Short answer: the marking on your watch is a water-resistance rating, written in bar, ATM or meters. One bar is roughly ten meters, so 3 bar, 3 ATM and 30 m describe about the same rating. Standards exist (ISO 22810 for water-resistant watches, ISO 6425 for divers’ watches), but advice on what you can do in water comes from the manufacturer, and the charts we read are far more cautious than the depth figure. Water resistance also fades as gaskets age, and a battery change can reduce it. Read your model’s chart, keep the crown pushed in, rinse the watch after sea water, and at each battery change ask for the gaskets to be checked and the water resistance tested.
If you have wondered whether “30 m” means you can swim with your watch, so have others: on a watch owners’ forum, the first reply to that question was “not suitable for swimming with.”
What the number on the case means
The Federation of the Swiss Watch Industry FH explains in its guide to water resistance that a watch described as “water-resistant” must comply with ISO standard 22810 and withstand a minimum excess pressure of 2 bars, “which corresponds to a depth of 20 metres”. ATM is a near twin of the bar: NIST’s conversion tables put one standard atmosphere at 1.01325 bar.
FH adds that a watch its manufacturer calls water-resistant or a diving model “must comply with international standards.” For water-resistant watches, that standard is ISO 22810:2010, which ISO lists as current. Its abstract says it “establishes the requirements and specifies the test methods used to verify the water resistance of watches.” When ISO announced the standard in 2010, it said a 30 m rating means “for all aquatic activities down to a depth of 30 meters, the watch case should not leak.” It added that manufacturers “may offer ratings to help consumers determine the sort of environment the watch can handle.”
What manufacturers say each rating allows
Manufacturers’ charts are stricter than the depth figure, and they differ. Here are two examples, not rules for yours.
| Marking | One manufacturer’s FAQ chart | A second manufacturer’s ratings page |
|---|---|---|
| “Water resistant”, no number | Not in the chart; a manual says “Please do not use it for swimming.” | “can withstand splashes and rain, but should not be submerged” |
| 30 m / 3 bar | Accidental splashes and rain only | “Washing hands” |
| 50 m / 5 bar | Adds swimming, yachting and showers | Adds “Light swimming” |
| 100 m / 10 bar | Adds “Bathing and Shallow Diving”, not scuba | Adds snorkeling, poolside diving and surfing |
| 200 m / 20 bar | Same as 10 bar: not scuba | Adds “Recreational Scuba Diving” |
| Diver’s watch, 200 m | Adds scuba diving | Not listed |
The first chart’s “Bathing” use is called “Skin diving” in the same manufacturer’s global FAQ, and one of its manuals says: “Do not wear the watch while taking a bath or a sauna.” FH is more relaxed: it says a watch with no number can be worn for daily activities “such as washing hands, showering”. FH’s own advice is to follow the manual: “It is therefore advisable to follow the manufacturer’s instructions”.
What makes a diver’s watch different
Divers’ watches have their own standard, ISO 6425:2018, which applies to watches “designed to withstand diving in water at depths of at least 100 m and equipped with a secured measuring system to indicate the diving time, which is visible in darkness.” FH adds shock and magnetic resistance and “a sturdy wristband” to the list.
So the first chart treats a 200 m watch and a 200 m diver’s watch differently. One of its manuals explains: “The various tightened inspections under simulated harsh environment, which are usually required for watches designed for scuba diving or saturation diving, have not been conducted on the water resistant watch with the BAR (barometric pressure) display.”
Why water resistance fades
A watch keeps water out with gaskets at the case back, crown and crystal, and they don’t last forever. The first manufacturer’s FAQ says: “A watch’s water resistance is not permanently guaranteed. It is affected by the ageing of gaskets or deformation of watch parts due to accidental shock.” The Japan Clock & Watch Association (JCWA), a trade body whose advice applies to its members’ products, explains on its water-resistance page: “With longtime use, the gaskets are affected by perspiration and moisture, so that their elasticity may deteriorate or they may become brittle and easy to cut. Therefore, it is recommended that you request to replace the gaskets during battery replacement or periodic checks.” It suggests checks “every two to three years.”
Another of the first manufacturer’s manuals says: “Once the case back is opened for battery replacement or other purposes, the original water resistant quality designed for the watch may deteriorate when it is closed.” It asks owners to “also request the water resistance test”, and for watches rated 10 bar or more to “be sure to have such test performed on the watch every time the battery is replaced.”
On the same owners’ forum, a poster wrote in 2013 that after a dealer replaced their battery, they went swimming and “noticed that the watch was wet inside”. A moderator replied that a free battery change meant “No gasket replacement and no pressure test”. That is one owner’s account, and the thread never established the cause; it doesn’t show how often this happens.
Crown and pusher habits
JCWA’s rule is “Do not operate the crown and buttons when moisture remains.” The first manufacturer’s manual says: “Do not turn or pull out the crown when the watch is wet.” The second manufacturer says not to “press any buttons under water unless your watch is indicated as 200m water-resistant.” Before the watch meets water, check that the crown is pushed fully in, or screwed down if it screws down.
Watch the crystal. The first manufacturer’s manual adds: “If the inner surface of the glass is clouded with condensation or water droplets appear inside of the watch for a long time, the water resistant performance of the watch is deteriorated.” If water gets in, JCWA says to “have it repaired immediately.”
Showers, hot water, saunas and soap
Sources disagree most about heat and soap. The first chart allows showers from 5 bar, yet the manual warns: “Steam, soap or some components of a hot spring may accelerate the deterioration of water resistant performance of the watch.” The insurer Jewelers Mutual, in its watch care guide, says: “Don’t wear it while showering (and be careful when washing your hands).”
In a 2012 forum thread, one poster asked whether the warning was “just a myth spread by online communities”; a moderator thought heat and humidity “can easily damage seals”, while another poster said his watchmaker had called it “a load of hooey”. Forum posts can’t settle the question, so if your manual rules out baths or saunas, take the watch off.
The manual also says faucet pressure “is high enough to degrade the water resistant performance of a water resistant watch for everyday life,” and its FAQ suggests washing a watch “in still water in a sink or a receptacle”.
Sea water and pool water
JCWA: “After swimming in the sea, thoroughly wash your watch with fresh water, and then completely wipe it to prevent it from rusting.” The first manufacturer’s FAQ agrees: “After using a water resistant watch in ocean water, wash it in fresh water and dry it with a soft cloth.” The care pages we read gave no separate rule for pool water, so check your manual. For rings and chains, our guide on when to take jewelry off explains why chlorine and salt water are hard on metals and stones.
Straps: leather, metal and rubber
A third manufacturer’s page warns: “Leather straps are not water resistant except where indicated, even if the watch head is water resistant”. JCWA’s care page adds that rubber and plastic bands “may crack, break, or deteriorate”, and that moisture and sweat left on metal bands “may cause rust”. For a watch that gets wet, leather is the strap to avoid unless marked water resistant. Our watch lug width and replacement band guide compares band materials.
What to ask
- When you buy: what is the rating, is it a diver’s watch, and what does the manual allow for swimming, showers and baths?
- At a battery change: will the gaskets be checked or replaced, will the water resistance be tested, and how long will that take?
- If the crystal fogs inside, keep the watch out of water and have it looked at.
Next step
Find the marking on the case back or dial and look up your model’s chart in its manual or on the maker’s site. Use that chart, not the depth figure, to decide what the watch can do in water. If the strap has worn out, our band guide covers measuring for a replacement.
