Water Resistance And Its Meaning
If you're old school like me and wear a watch, take your watch off and take a look at either the dial (face) or the back of the watch. Look for anything that says water resistance, or a number like 30M, 50M, 100M, or perhaps it is measured in feet - '330ft'.
You probably recognize what that is right? That is the water resistance rating of your timepiece. But a lot of people do not know what that actually means. Often times they assume that is how deep their watch can go before running (swimming?) into problems. Unfortunately, the watch industry has done a poor job of communicating this because that rating really has nothing to do with depth at all, practically speaking. If it says "Water resistant to 30M" on the back of your watch, it precisely means that you CANNOT go 30 metres deep with that watch. And that, I'll admit, can be confusing.
Here are 3 things you probably do not know about water resistance as it pertains to timepieces.
1. They are not talking about depth.
Then why do they measure it in metres/feet? It doesn't really make a whole lot of sense and is pretty confusing at face value. When a watch says water resistant too, let's say, 100M, the company is not actually saying it can go 100M deep. What they are saying is that it can withstand pressure equal to 100M deep. This is an important distinction. If you put your watch in a bucket that was 100M tall and full of water, and the watch was sitting perfectly still at the bottom, and the water was perfectly still, that would be the measurement of pressure at 100M deep. However, in the real world, typically the water is moving and the wrist that the watch is attached too is moving. As soon as one (or both) of those start to move, there is greater pressure being applied to the watch.
Some watch companies are starting to display their water-resistant ratings in BAR or ATM (atmosphere). This is a much more honest way of showing how much resistance a watch has to water pressure. Unfortunately, most people do not know how many BAR/ATM's they would need to actually go swimming with a watch on. And to be fair, most people do not know how many metres/feet are required for swimming either. Here is some simple math for you: 1 bar = 10 metres. 3 bar = 30 metres. 10 bar = 100 metres. You should not take your watch swimming unless it says 10 bar or 100M or more in water resistance. Anything less and basically it can handle humidity, rain, or splashes of water while you're doing the dishes.
2. Warranty does not cover water damage.
There is not a watch company in the world that cover's water damage. The most waterproof watch that we carry, the Rolex Deepsea, which is waterproof to an astronomical depth of 3900M - yes, that is 3.9 kilometres - is not covered under warranty should you get water inside the watch. Yes, there are many watches that are marketed as sea-faring pieces, with names like Seamaster Planet Ocean, Aquaracer, Aquatimer, Sea-Dweller, and Marine Star, but unfortunately, none of these will be covered under warranty should you get water inside the watch.
So how does water get inside of a seemingly "waterproof" watch?
Basically, there are two ways we see this happen most: (1) user error and (2) gasket failure. User error in that if your watch has a screw down crown, sometimes people accidentally forget to screw it back into the case and then decide to take a shower. We see this happen a lot around the time of year when we "spring forward" an hour or "fall back" an hour on the clock. The other way is gasket failure. Most watches do not have screw down parts (see my third point for more on that) and because of this, the only thing holding moisture out of the timepiece is a rubber gasket. Over time these will dry out and crack. And you will only know this once water is already inside the watch and the damage is done.
3. Screw down parts are a must.
As mentioned previously, don't take a watch in the water unless it is at least 100M or 10 bar rated for water resistance. But I would probably go even further than that. Personally, I would not take a watch into water unless it has a screw on case back, a screw down crown, and if it is a chronograph, screw down pushers, and a sapphire crystal. When a watch possesses all of these features, it really is a waterproof timepiece. Having everything screw into the case ensures that no water will get inside the watch, and a sapphire crystal adds significantly more strength should you accidentally knock the crystal on something while swimming.
Rolex is the only brand I know of that actually uses the word "waterproof" for their watches, everyone else seems to use the words "water resistance". The reason for this, I believe, is because the entire case for all the Rolex watches are built in such a fashion that everything screws into it - the word "Oyster" adornes virtually every piece for a reason. The case back, the crown, redundant gaskets and of course a sapphire crystal. They actually water test their watches with the crown open to a certain pressure to make sure that even if you accidentally leave the crown open in wet environments, there is still a good chance you might not get water inside your watch!
One last thing. Beware of humidity! Most people forget about this with watches, but humidity is a killer. If you leave your watch on the counter while taking a shower, it is possible for the humidity from the shower to get into the watch. And should this happen, get your watch in for repair ASAP. The longer you wait, the more likelihood rust will start forming, and once this happens the repair will be significantly more costly. Should you get water or humidity inside your watch, a trained watchmaker will have to completely dismantle the movement, dry off each piece, apply new oils, and replace all gaskets. This is really the only way you can be sure that all the water has been removed from your watch and that rust will not form on the parts inside.