Discover what your watch’s waterproof rating really means and the mechanical wonders behind it
The vocabulary of watches can sometimes sound quite confusing. But while few people actually know what a “column wheel” is or what “equation of time” means, those terms actually have exact definitions. But, the seemingly simple “waterproof”— and its close cousin “water-resistant”—has caused quite a lot of confusion.
If it says “30M” on the dial of the watch, then you can take the watch diving as long as you don’t go deeper than 30 meters, right? No? Then how about just swimming in the pool? Also no? What does “30M” mean, then? Well, read on...
Before we go into the nitty gritty details about how waterproofing—or water resistance—works in watches, perhaps we can start with a brief look into what the typical depth ratings actually mean.
If a watch doesn’t say “water resistant” or has a depth rating, then it should never come into contact with water. End of story.
30M/3 atmosphere/3 bar
A watch with “30 meters” inscribed on its dial can survive being splashed when you, say, wash your hands.
50M/5 atmosphere/5 bar
This is the kind of watch that you can wear in the swimming pool. Still, it’s best taken off before you dive into the water. And don’t even think about doing any actual diving while wearing it.
100M/10 atmosphere/10 bar
Finally, something that you can take while snorkeling or swimming for extended periods. Still, this is not a diver’s watch.
200M/20 atmosphere/20 bar
Now we’re starting to brush the surface of diver’s watch territory. Might survive a shallow dive using scuba gear, but better not risk it.
300M/30 atmosphere/30 bar
While not technically a diver’s watch, these usually have an escape valve that makes it safe for actual diving.
Diver’s Watch/ISO 6425
If you find the inscription “Diver’s Watch” or “ISO 6425” on a watch, then it’s certified for deep diving. If there’s no specified depth behind it, this usually means that the watch can handle depths of up to 100 meters. An actual diver’s watch will usually feature increased tolerance against salt water, magnetic fields and shock as well.
Now that we’ve got the ratings cleared up, let’s continue to the “how” and “why” parts.
A lot of people, when realizing that a watch that says “Water Resistant 30 meters” can’t even survive a plunge of three meters might feel that the labeling is misleading. And, for sure, it can be quite confusing. That being said, you have to know that there are actual standards governing these ratings.
First and foremost is the use of the term “water-resistant” as opposed to “waterproof.” Logically speaking, the reasoning behind this is that no watch can truly be claimed to be totally impervious to the effects of water. That is, of course, only conceptually possible. Second, there is a legal precedence to this as well, namely a ban on the term “waterproof ” by the U.S. Federal Trade Commission or FTC dating back from the ’60s. The FTC pointed out that “the word ‘proof ’ connotes a measure of absolute protection that unfortunately does not exist with respect to
“an actual DiveR’s watch will usually featuRe incReaseD toleRance against salt wateR, magnetic fielDs anD shock as well”
watches, especially over prolonged periods of time.” It should perhaps come as no surprise that this regulation came about after several lawsuits against watchmakers.
Today, watchmakers follow a set of standards. There’s ISO 22810:2010 for watches that are merely water resistant and the aforementioned ISO 6425:1996 for diver’s watches.
As for what actually keeps water out of a watch, several factors come into play. First up is construction of the case and, particularly, how the caseback is attached. The least water-resistant are snap-on caseback. In this setup, the slightest nick on the case body or the smallest deformity on the gaskets can allow water to rush into the watch. And it’s not a matter of if it happens but when. Watches with snap-on casebacks are rated—at most—for 30 meters. (Once again, please refer to the list in the previous pages to see what “water resistant 30 meters” actually means.)
Casebacks that are fastened with screws are much better, but they are still vulnerable as soon as there’s a problem with the gaskets. Maximum water resistance for this type of construction would be 100 meters. Finally, we have screw-in casebacks which are treaded and screwed onto the case. This is the type that you’ll usually find on actual diver’s watches for professionals.
Then there are the aforementioned gaskets. Sometimes dubbed O rings, these are employed as watertight seals at the joints where the crystal, caseback, crown and pushers (if any) meet the case. Commonly used materials include rubber, nylon, silicon and Teflon. As with any kind of seal in a mechanical contraption, gaskets will wear away and break down with time.
“when it comes to wateR Resistance, useR BehavioR anD maintenance aRe just as impoRtant as BuilD quality’”
The Achilles heel of any water-resistant watch, however, is the crown. Or, to be exact, the hole on the case for the stem of the crown. The gasket on this part is constantly compressed, stretched and chaffed every time the crown is pushed, wound or turned. A screw-down crown, however, is threaded and designed to screw shut to the threading of the hole—or technically tube—on the case. Obviously, this is an essential feature on any watch that will keep you company as you swim or dive.
And now we come to the crux of the matter. A watch’s water resistance capabilities are tested in optimum conditions: Fresh gaskets, static (i.e., still or calm) water, stable temperature, etc. They are also tested right after assembly. By the time they leave the factory and arrive in stores, months—or even years—could have passed. When we reach this point, it’s no longer a matter of ISO standards but of the individual quality standards of each brand.
When we’re talking about mechanisms like tourbillons, chronographs or calendars, there is usually little need to talk about how we— the wearer—treat the watch. When it comes to the water resistance qualities of watches, however, user behavior and maintenance are just as important as the build quality of the timepiece. So, for this edition of our Mechanisms column, we’re compelled to compile a list of basic tips regarding the wearing of watches near or in water.
Err on the dry side
Some watches are actually tested for beyond their rating. Still, you should always heed the safe operating parameters of your watch and follow it religiously. Of course, it’s always best if your watch simply stays outside the bathroom, beside the pool or on the boat when you go diving.
Maintenance is key
If you have a watch that is supposed to work under water and you intend to use it that way, have it tested on a regular basis. Also, make sure that you have the watch maintained by somebody reliable—preferably at the brand’s official service center as it is all too easy for an amateur watchmaker to, say, puncture a gasket with the very tweezers used to replace said gasket.
Be wary of the temperature...
Sudden changes in temperature can adversely affect the integrity of your watch’s gaskets. That being said, rubber gaskets can easily withstand water at temperatures of 100°C and silicon is even more resilient. So, wearing your watch (rated 30 meters or more) in a hot shower is actually okay. On that note, the chemicals found in soap and other grooming products can theoretically harm rubber gaskets as well, but the quantities required for this to happen is much, much higher than what is used on a daily basis.
Push it down...
Before you dive into a pool or into the sea, make sure that the crown is pushed in and—if you have a watch with a screw-down crown—securely tightened. And then, do not operate the crown or any pushers while under water.
Above all else, remember that a good watch is an investment. Pick the right one, take good care of it, and it can accompany you no matter how far—or how deep—you go. Terms and conditions apply.
ocean explorer Fabien Cousteau wearing a Seiko Prospex diver’s watch Opposite page the omega seamaster 300m
The Ulysse nardin Diver Chronometer monaco Limited edition worn by underwater photographer Fred BuyleOpposite page Close up of the crown of a Harry Winston ocean Dual-Time retrograde