How Watch Pressure Testing Actually Works

The first waterproof watch to hit the world market, the Rolex Oyster, was released nearly 100 years ago in 1926. This landmark product rose to world renown in 1927 when Mercedes Gleitze wore it as she became the first British woman to swim across the English Channel.

Since then, water-resistant watches have become staples in the lives of divers, swimmers, and athletes, as well as those who value high-end, high-quality products that can withstand life’s unpredictable nature. Suunto, Scubapro, Cressi, and Mares are just some of the big names in the dive computer industry, while Casio, Citizen, and Seiken straddle the line between dress and dive watches.

These manufacturers are all famed for their water-resistant watches—but what does “water-resistant” really mean? It’s a question worth asking when you’re contemplating any high-value product. Let’s take a look.

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The first thing we need to understand is how pressure changes as we go from air to underwater. Hydrostatic pressure, i.e. the force per unit area exerted by liquid (water) on an object, increases the deeper we go. At 10m deep, the pressure is double what we experience at the surface. For every 10.06m (33 feet) we descend, pressure increases by 1 atmosphere (1.01 bar or 14.69 PSI). 

This gives us some idea of what our watches must be able to withstand in order to continue to function when we swim, snorkel, or dive. If you’re into water-resistant watches, you may have come across this guide:

• 30m: splash-proof

• 50m: safe for brief, shallow swims

• 100m: safe for swimming and snorkelling

• 200m: safe for diving

• 300m-500m: suitable for professional diving

It’s a useful guide—but it’s only a guide! Most dive watches and dive computers are water-resistant at 100m; this adheres to the ISO 6425 standard and means the watch is suitable for recreational diving. Many dress watches, sports watches, and dive watches fall into this category, meaning you have a whole host of options when it comes to choosing the size, style, and price-point that’s best for you. 

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Once you’ve bought your watch, of course, it’s time to look at how to maintain it. In addition to monitoring wear and tear, battery life, and salt/dirt build-up, testing a watch’s resistance to water is one of the most essential parts of dive watch care. This is done using pressure tests. 

There are two types of pressure tests: dry and wet. Dry tests, also known as vacuum tests, are considered “safer” due to the absence of water, but are only really useful in determining if there’s a leak, not in measuring the pressure a watch can handle. For that, you need a wet test.

Wet testing allows testing at specific pressures to give an exact measurement of whether a watch remains water-proof at a particular pressure. In simple terms, it works by pressurising the air within the chamber so that, if there’s a leak, air will enter the watch. Once the watch is lowered into the water and the pressure is released, any air within the watch will leak back out and bubbles will appear in the water. If no bubbles appear, your watch has passed the leak test!

Most watch manufacturers recommend pressure testing once a year, and always after battery replacement. Discovering a leak during—or after—a dive is not something anyone wants to experience. Being proactive about maintaining your dive watch is the best way to ensure its long life.

Is your watch due for a pressure test or battery replacement? Book your service now.