Large Blue dive watch with blue bezel and three silver subdials with red GMT hand and long thim lumed main hands, on a blue rubber strap.
Hamish Robertson, Sep 9 2022

What makes a watch Waterproof?

What makes a watch Waterproof?

Almost everyone wants their watch to be waterproof. We all expect that a new watch will be waterproof whatever the price point or watch type. But what makes a watch waterproof?

Waterproof or Water Resistant?

Modern advertising laws mean watch companies cannot advertise their watches as waterproof. A watch made of lots of different case parts means there are gaps that water can get into, especially if the watch is old or hasn't been serviced for a while. Watch companies instead use the term Water Resistant. Use of this term is now limited only to those watches which conform to the International Standard 22810, explained further below.

A Waterproof Dive Watch from UK brand Bremont. This watch is water resistant to 200 Metres Depth.

A Waterproof Dive Watch from UK brand Bremont. This watch is water resistant to 200 Metres Depth.

What does Water Resistant mean?

Water Resistance ratings are measured in units of Atmospheric Pressure, known as Bar. When you stand at sea level on the surface of the Earth you are experiencing, on average, 1 Atmosphere of pressure. The Symbol for this is "atm". Since pressure is measured with a device called a Barometer, units of pressure are also often called "Bar", and you experience 1 Bar of pressure from the atmosphere.

Very roughly speaking, there is a ratio of atmospheric pressure to water pressure of 10m equals 1 atm. So if you go 10 metres underwater you are experiencing an additional 1 atm or Bar of pressure.

Watch designers can choose how waterproof to make their watch. The design requires the case construction and gaskets to create a very tight seal, whatever its shape. It is the strength of the case material and the use of these gaskets (usually made of rubber), that determine the water resistance of the watch. A gasket is usually just a rubber ring that helps press into the gaps between the metal and create the seal. The important thing to know is that these gaskets degrade over time and need replacing regularly to ensure your watch remains fully water resistant.

These rubber gaskets are placed inside the watch case before the case back is replaced to ensure a watertight seal is created. It is the gasket that prevents water entry, not the screw thread or other closure mechanism.

These rubber gaskets are placed inside the watch case before the case back is replaced to ensure a watertight seal is created. It is the gasket that prevents water entry, not the screw thread or other closure mechanism.

Here is a table of use that people have traditionally referred to when thinking about the different uses, which will apply to vintage watches that have been fully serviced and tested. For example, Rolex will service a 60-year-old Submariner that is rated at 200m so that it is equal to that rating today if it can. However, if you have a vintage watch and do not know its service history, it is a very bad idea to use it as the table lays out below. Rolex is an interesting example as there are many professional divers who successfully used the same Submariner dive watch across their whole career without problems, although they did get it regularly serviced.

Table showing water resistance levels by stated depth rating.

Table showing water resistance levels by stated depth rating.

Water Resistance in Modern Watches

To clear up the confusion that historical water resistance ratings created, and also to make sure that watch companies do not claim their watches are fully waterproof, the industry adopted two ISO standards for water resistance. These standards are now required for any watchmaker to meet to claim their watch is water resistant. The standard applies regardless of what the watchmaker writes on the dial.

A modern Swatch from the current range. This is sold as water resistant to 3 atm, and is therefore rated to modern ISO standards. This means that it is suitable for almost all water-related activities, including swimming.

A modern Swatch from the current range. This is sold as water resistant to 3 atm, and is therefore rated to modern ISO standards. This means that it is suitable for almost all water-related activities, including swimming.

The ISO Standard for Water Resistance and Divers Watches

The International Standards Organisation exists to set industry-wide standards for all aspects of manufacturing and services. It has a range of standards for watchmakers including some on Water Resistance. They are very helpful and were last updated in 2010. Most notably, they include tests of activity, and the watches are tested up to 2 Bar. This means that they will be useful for almost any water-based activity other than deep scuba diving. The Standard for Water Resistance is ISO 22810:2010.

The Divers Watch ISO standard is conducted including activity to a depth of 10 Bar, or 100m or below, thus also including almost all leisure and commercial diving activities. The Standard for Diving watches is ISO 6425: 2018

You can ask a manufacturer if they make these watches to these standards, and if they do then you can be sure your watch will be water resistant for almost any activity you require. If the watchmaker claims it has a Depth rating of 1000m for a Dive Watch but it does not also claim the watch meets the Divers' Watch standard, then caution is advised if you wanted to use the watch for diving.

This Diver's watch from Helm has a rating to the full Diver's ISO 6425, and displays this proudly on the dial. This could be used for any kind of diving that people undertake down to 300m.

This Diver's watch from Helm has a rating to the full Diver's ISO 6425, and displays this proudly on the dial. This could be used for any kind of diving that people undertake down to 300m.

Conclusion

Almost any watch that is sold with a water resistance rating today should be held to a decent waterproof standard. You should ask if you are unsure, and if you want to really make sure of a Dive Watch's status, look for one expressly marked Diver's 200m on the dial. There are an enormous range of different watch designs and water resistance ratings out there, and a small amount of action could save you a lot of money. We at The Watch Collectors' Club recommend you check before you dive! If you are interested in learning more about how watches are made waterproof and what dive watches look like, please join one of our regular watch events, or send us any questions you may have.

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