Waterproof vs Water Resistant Watches

You’ve probably come across various terminology used to indicate water resistance of wristwatches.

But what does “Waterproof” really mean? Or “Water Resistant”?

Not to mention those marks “50m”, “100m” and so on.

I’ll take a closer look into that and more in this article.

“Waterproof” vs “Water Resistant”

First and foremost no watch is 100% resistant from ingress of water. The different ratings are merely meant to describe how resistant the watch is.

The better rating, the more resistant.

This is probably one of the reasons why the Federal Trade Commission banned the use of the term “Waterproof” in advertising in the watch industry in the late 1960s.

The term “Waterproof” implies that a watch can’t leak under any circumstance.

But this is not the case.

According to the Merriam-Webster Dictionary the definition of the word ‘Waterproof’ is given as: “impervious to water”.

In the watch industry (or any other industry for that matter) ’Waterproof’ does not mean impervious to water infinitely. The term ‘Waterproof’ is rather to be perceived as an indication of the best possible degree of water resistance.

Have you noticed that you seldom come across a watch marked with a water resistance rating of 30m?

This is because a watch of this class is quite vulnerable and preferably shouldn’t be exposed to water at all.

A watch marked with “Water Resistant 30m” or similar allows for contact with water but not immersion.

You can also wear it while washing up or walking in the rain. But that’s about it.

More about that in the following.

Water Resistance Explained

“Water Resistant” is a common mark stamped on the dial and/or the case back of wristwatches to indicate how well a watch is sealed against the ingress of water.

Usually an indication of the static pressure will be indicated as well.

Typically, this indication is given in meters or ATM or bars.

(in the United States sometimes also in feet)

The way they relate to each other is simple:

50 meters = 5 bar = 5 ATM ( = approx. 165 feet )

It’s a widespread misconception that a watch rated “Water Resistant 50m” can be submerged in water to a depth of 50 meters and be expected to survive.

What it really means is that a sample of the newly manufactured watch has been lab tested under static pressure comparable to the pressure under still water at 50m depth.

And this only for a short period.

When you move your watch under water while swimming, or jump into the pool, the pressure varies and that’s something the test does not take into account.

ISO 2281

In 1990 the International Organization for Standardization issued a standard for water-resistant watches intended for ordinary daily use.

The standard also prohibited the term waterproof to be used with watches.

Watches certified under ISO 2281 are not intended for submarine diving.

ISO 2281 includes a number of tests for water resistance of watches.

I will just mention two of them here:

1) Resistance when immersed in water at a depth of 10 cm. Immersion of the watch in 10 cm of water for 1 hour.

2) Resistance of operative parts. Immersion of the watch in 10 cm of water with a force of 5 N perpendicular to the crown and pusher buttons (if any) for 10 minutes.

ISO 6425

A similar standard for diving watches was introduced in 1996.

ISO 6425 defines a diving watch as: A watch designed to withstand diving in water at depths of at least 100m and possessing a system to control the time.

The testing of the water resistance in ISO 6425 is fundamentally different from non-dive watches because every single watch has to be tested.

Besides, diving watches are tested in static or still water under 125% of the rated (water) pressure.

Essentially this means that a watch marked 200m is water resistant to a depth of 250m in static water.

As you can imagine the ISO 6425 standard involves a much more comprehensive testing procedure.

For example a diving watch is immersed in water to a depth of 30±2 cm for 50 hours.

You can read more about the specific details of the testing procedure contained in ISO 2281 and ISO 6425 here.

Note: It may be worth mentioning that testing diving watches for ISO 6425 compliance is voluntary, so not every manufacturer present their watches for certification according to this standard.

Water Resistance Guide

30 m

Allows for accidental splashes but not suitable for swimming.

50 m

Suitable for everyday use and bathing but not swimming, diving, snorkeling or water sports.

100 m

Suitable for swimming and snorkeling but not suitable for high board diving or sub-aqua diving.

200 m

Suitable for all high impact water sports and scuba diving at depths not requiring helium gas and/or decompression.

300 m

Suitable for all high impact water sports, scuba diving and saturation diving.

General Advice

Regular Service Check

If you intend to expose your watch to water often, it’s a good idea to have your timepiece regularly serviced.

A watch pressure tested to 50m may not be equally resistant to water ingress 2 years later because the water resistance will reduce over time.

Have it water-tested once a year and you should be safe.

Showering and Swimming

Don’t wear your watch while showering. To my mind there’s no obvious reason to do so while there’s several good reasons to not do so.

Over time, the hot water can deteriorate and crack the rubber seal.

Certain chemicals in water can damage the watch seal like perfumes, aerosol sprays and other cosmetics.

While in Water

Do not open, wind or operate the crown.

Do not press the buttons of a chronograph, unless otherwise stated by the manufacturer.

My Personal Buying Advice

There’s a bit of confusion among watch bloggers and retailers regarding water resistance to a depth of 50m.

Some claims this rating makes a watch suitable for swimming, others advice against, meaning we are sort of on a verge here.

The reality is there is no such thing as a 100% waterproof wristwatch, it’s all about reducing the risk of water ingress. In other words, the better rating, the better water resistance.

If you plan to buy a water resistant wristwatch and you know you will be wearing it a lot while in contact with water, e.g. in connection with fishing trips, sailing or other activities involving shallow contact with water, make sure to purchase a watch preferably with screw-down crown and rated at least 100m.

You may not be exposing your watch to water under high pressure too often, but it’s still better to be safe than sorry, isn’t it.

For more demanding activities like swimming and snorkeling, I would go for a watch rated at least 200m and with screw-down crown.

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Claus is a laboratory technician, autodidact guitarist, songwriter, music publisher, co-founder of App Division ApS, dad of fraternal twin boys, Sci-Fi lover, incarnated Mike Oldfield fan, pro world peace and an incorrigible coffee addict.

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