Blog: Water Resistance

Date: 1 April 2019

Copyright © David Boettcher 2005 - 2023 all rights reserved.

I make additions and corrections to this web site frequently, but because they are buried somewhere on one of the pages the changes are not very noticeable, so I decided to create this blog section to highlight new material. Here below you will find part of one of the pages that I have either changed or added to significantly.

The section below is from my page about Looking After a Mechanical Watch.

If you have any questions or comments, please don't hesitate to contact me via my Contact Me page.

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Water Resistance

The term “waterproof” is not used for watches today, recognising that such an absolute standard cannot be achieved. Instead it is replaced by “Water Resistant” along with a pressure rating in atmospheres and metres or feet of water, which gives an idea of just how water resistant the watch is. There are two international standards that regulate the testing of watches, ISO 22810:2010 Horology - Water-resistant watches, and ISO 6425:1996 Divers' watches.

The normal pressure of the atmosphere atmosphere at sea level is about 14½ pounds-force per square inch (psi) or 1 bar - a standard atmosphere is 1.01325 bar. This is equivalent to a column of mercury in a barometer of 29.92 inches or 33.9 feet of water, which is about 10.3 metres of water. So one bar pressure is equivalent to about 10 metres water gauge or depth under water.

A watch that is described as water resistant might be less waterproof than you might think. A watch rated at 3 atmospheres (3 atm) or 30 metres / 100 ft water depth might seem at first sight to be more than adequate for swimming or showering. After all, you are hardly likely to get 100 feet deep in a swimming pool! However, this rating is a static pressure that the watch was tested to when it was new. There are all sorts of reasons why a watch of this rating is not suitable for swimming, such as the pressure is increased by movement - diving into water, or the jet from a shower create a much higher dynamic pressure. And that pressure rating was recorded when it was new - over time the seals deteriorate and need to be renewed. Unless a watch has been tested for water resistance within the last year, you should assume that it is NOT water resistant. If it has been tested, the certificate will tell you its level of water resistance.

1. Watches rated at 3 atmospheres / 30 metres are resistant to rain or splashes from hand washing, but are not suitable for swimming or wearing in the shower.
2. A watch rated at 5 atmospheres / 50 metres will tolerate gentle showering, but not power showers or jumping or diving into water.
3. For swimming, water resistance of at least 10 atmospheres / 100 metres is required.
4. For sub-aqua, water resistance of at least 20 atmospheres / 200 metres is required.

Watches don't remain water resistant for ever. Before a watch described by the manufacturer as water resistant left the factory, it was tested and carried a time limited guarantee. When it was subsequently serviced at the specified interval, the water resistant seals should have been renewed and the water resistance tested and guaranteed again. A factory licensed watchmaker would do this, but they are expensive and people often shop around for a cheaper price.

Machines for testing water resistance are relatively expensive, and one of the easiest things to leave out that doesn't appear to affect the going of the watch is changing the seals. Both of these factors make the job cheaper, and the receipt usually has “water resistance not tested or guaranteed” stamped on it so there is no mistake. Such a watch must never be exposed to water, even when washing hands it should be taken off first.

Many years ago I entrusted a valuable watch of mine to a swanky jewellers in a nearby posh town, who described themselves as specialists in elite jewellery and prestige Swiss watches. They persuaded me that it was not necessary to send the watch to the manufacturer's service agent because their own service department could do it just as well, and more quickly and cheaply. They didn't change the case seals before testing the watch for water resistance, which it naturally failed and they noted on the invoice. But in the process water had got into the case and that evening I saw droplets of water condensing inside the glass. Even though I immediately took the back off and pulled the movement out, the dial, hands and movement were all ruined. They were replaced by the manufacturer's service agent, who also changed the case seals and guaranteed that the watch was waterproof. It was a very expensive lesson.

If you are concerned about the water resistance of your watch, a very simple test is to place an ice cube on the glass and, after a while, look for signs of condensation on the inside of the glass. A very small amount of condensation is acceptable, after all, all air contains some moisture in the form of humidity which will have been trapped inside the watch when it was closed up. But more than a small trace is a cause for concern and you should get it professionally checked.

The bottom line: water getting into a watch can be a disaster. The steel parts rust and the watch can quickly become unrepairable. Economy here can easily turn out to be false economy! If your watch is not highly water resistant, or you are not sure how water resistant it is, don't take chances, keep it dry. If you want to splash about in the shower, swimming pool, or in the sea, get a properly water resistant 100m+ watch, get it tested and the seals checked and replaced regularly, and then don't worry about it.