You will have noticed just as I have that summer is coming, complete with sunshine, rising temperatures and terraces filling up! Despite a complicated context, we all want (and need) a holiday and whether it takes place on the other side of the world or on the shores of Lake Neuchâtel, one thing is for sure: we will enjoy a good swim as soon as the opportunity arises!
Be it in a pool, river, lake or sea, swimming is probably one of the most popular summer activities for holidaymakers.
But why talk to you about holidays and swimming in a watch column? Well, quite simply because for some of you, the watch that will accompany you on holiday will also benefit from refreshing dives or even those of the “splash bomb” variety, making tidal waves in the pool. And your watch had better be water-resistant, because a watch that lets in water ends up like this:
I promise I’m not trying to scare you! Instead, I want to make you aware of a truly important subject, which as a watchmaker I feel is all too often neglected: watches’ water-resistance. So before talking to you about water-resistance and getting to the heart of the matter with technical elements that re worth knowing, I first want to reassure you: nothing is impossible to the valiant (nil volentibus arduum). This watch has been restored, is keeping time with remarkable accuracy and is now totally water-resistant.
What is water-resistance?
From a watchmaking standpoint, water-resistance is a watch’s capacity to resist letting in an extraneous element such as air, or above all, water. This level of resistance is expressed by a unit of pressure (in bars), depth (in metres, generally corresponding to the pressure exerted by water at the said depth), or in atmospheres, a unit we will decipher right away!
"Normal" pressure at sea level corresponds to what we call "1 atmosphere" and this value is close to 1 bar. From the outset, one can thus consider that when you read that a watch is resistant to 1atm, it is resistant to a pressure of 1 bar. At the end of the day, resistance to ambient air is a good thing, but it does not really indicate a water-resistance value.
There is an ISO standard (no. 22810) on which the various watch brands base their definition of a watch’s water-resistance. Basically, the ISO 22810 standard defines a watch as being water resistant when it resists an overpressure of 2 bar. Going back to what we said earlier, 2 bar corresponds to the pressure exerted in an aquatic environment at a depth of 20 metres. This doesn't necessarily mean that you can dive to 20 metres with it, but it does give us essential information about its resistance to this level of pressure.
I don't know about you, but whenever I descend to a depth of more than 2 metres while swimming, my ears hurt terribly and I come up to the surface as soon as I can. This pain is due to the increased pressure on my eardrums. The eardrum is the thin membrane that separates the outer ear from the inner ear and is about one tenth of a millimetre thick. It is difficult to compare an eardrum and a watch, but this little comparison helps us understand that the deeper you go, the more the pressure increases. Thus, according to the ISO 22810 standard, a so-called water-resistant watch can resist a pressure of 2 bar (which corresponds to the pressure at a depth of 20 metres in water), which is already quite good.
How is a watch built so as to be water-resistant?
As you can see, there are several degrees of water-resistance. At 2 bar, one can indeed imagine that you should be able to wash your hands or the dishes with your watch on your wrist without any problem (sorry gentlemen, you can no longer use your watch as an excuse to avoid washing-up). Your watch will also survive a shower or a bath, as long as its water-resistance has been confirmed by a certified watchmaker.
So how can you be sure that your watch is water-resistant? To answer this question, we must first take a closer look at how a watch case is built and how it will react when subjected to high pressure.
Glass Gasket (seal) - Bezel - Case middle Crown tube - Gasket (seal) - Crown - Gasket (seal) - Caseback
The watch case is thus composed of assembled elements. As shown in the above diagram, a system of dedicated gaskets (seals) serves to connect the various parts of the watch in just a way as to prevent water from penetrating these sensitive areas. There is a seal between the glass and the case middle, held by the bezel; also around and/or inside the crown tube depending on the manufacturer; sometimes also in the crown; and finally between the case middle and the back.
What happens when pressure increases?
If you take a balloon and squeeze, you apply pressure which distorts and squashes it. In the case of a watch, exactly the same thing happens when it is subjected to a certain amount of pressure, yet the deformation will be imperceptible to the naked eye. One can nonetheless imagine that the deformation of the watch case elements will create a possible passage leading towards the sensitive areas (glass, crown, back). This is where the seals come into play by filling – thanks to their elastic properties – the spaces potentially created by the deformation generated by the pressure. Please note that we are talking about deformations measurable in microns, which is why this phenomenon is imperceptible to the naked eye.
Watch case without any pressure
Deformation of the watch case under pressure
So how water-resistant should a watch be for what activity?
3 atm – 3 bar – 30m
If we interpret what has been said above, this means that a watch that is water-resistant to 3 atm (or 3 bar) will deform at this pressure without this deformation allowing water to penetrate. The vast majority of watch brands consider that from 3 bars, a watch is water-resistant and can be worn for surface swimming. I quite agree with this opinion, even if many other factors are to be taken into account, such as temperature variations, typically corresponding to the 45 degrees easily reached when exposed to the sun and the coolness of a mountain river water. In the end, it's water-resistant on paper, but everyone is wary...
5 atm – 5 bar – 50m
I was talking earlier about dives and splash bombs. These two moves of which I am particularly fond are particularly interesting because of the violence of the entry into the water. In the watch industry, we are accustomed to talking about static pressure and dynamic pressure, and numerous demonstrations have proved on paper that dynamic pressure (corresponding to the movement that can be made in water, which should increase the pressure exerted on the watch) is ultimately negligible. On the other hand, the violence of the transition from air to water is the element that makes me advise you to be very careful when you enter the water with a watch that is water-resistant to 3 bars. It is in this spirit that I would recommend a minimum water-resistance of 5 atm (or 5 bars) for more ‘explosive’ aquatic activities.
10 atm – 10 bar – 100m
When a watch presents technical characteristics such as a screw-lock crown and a screw-down back, it generally means that the manufacturer has implemented additional means to improve and optimise the water-resistance of the timepiece. A screw-lock crown will have the advantage of reducing the risk of water seeping in through the crown by blocking its position. The majority of watches with this type of feature are water-resistant to at least 100m.
In general, as soon as a watch is water-resistant to 100m, one can be fairly confident of its ability to withstand prolonged immersion, even at depth.
A quick aside on divers’ watches, as these are designed specifically to meet the ISO 6425 standard, which defines divers’ watches as those designed to withstand diving in water at depths of at least 100m and equipped with a secured measuring system to indicate the diving time. Divers’ watches are tested in static immersion at 125% of their actual resistance. In concrete terms, a divers’ watch that is said to be water-resistant to 200m will have been tested at a pressure equivalent to a depth of 250m (25 bars) and the tests are carried out on all watches and not merely on a sample batch! Numerous other tests are planned for delivering the ISO certification, thereby enabling the standard to provide an even better guarantee of these watches’ water-resistance in an aquatic environment.
To cut a long story short, a divers’ watch is designed to be immersed to a depth of over 100m in extreme conditions. There is no fear that your watch will let water in, so if you have decided to invest in a divers’ watch: make the most of it!
How do I know if my watch is still water-resistant?
The most important elements that make a watch water-resistant are the precision of the adjustments of its case and the quality of the seals used. A watch’s water-resistance may deteriorate in terms of one of these aspects.
A violent impact can potentially cause deformation of the watch case or sensitive parts (glass/bezel, crown and caseback) and create a potential entry point. Over time, seals will tend to dry out and lose their elasticity. In such a case, if the watch is put under pressure, the seals will no longer do their job and water may seep in.
For a contemporary watch that is less than five years old, with no signs of having sustained shocks or falls, I would say that there is theoretically not much risk that the initial water-resistance of the watch could be impaired. On the other hand, if the watch is dropped or subjected to a violent shock, it may be wise to go to the shop to have the water-resistance of your watch checked.
Once a watch is five years old or more, we recommend that you have it tested for water-resistance every two years by a simple air pressure test designed to detect any possible deterioration.
Air pressure test
In the event of a negative result, further water-based tests can help to locate a possible leak and guide us in solving the problem. The replacement of seals or work on the watch case may sometimes be necessary and we are more than willing to assist you with this type of work.
Negative pressure immersion test
The final word
This summer, avoid when extra stress when swimming with your watch by first coming in to have its water-resistance checked in our boutique, thus enabling you to enjoy your holidays free from any worries in this respect.
I hope that this watch column dedicated to the water-resistance of watches has answered some of your questions. We are available in the store to answer any other queries you may have and to check your watch’s water-resistance.
Happy holidays to all!