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Water Resistant vs Waterproof: The Ultimate Guide

October 11, 2021

Quick question: Suppose your watch has a water resistance rating of 100m...does that mean you can dive without any effects? No.

For timepieces, water may be public enemy number 1. Yet watch snobs, beginners and enthusiasts still require a clear explanation about what precisely is water resistant and waterproof. 

You may think these terms are cut from the same cloth but they don’t have the same meaning. Stick with us to find out. So what is the difference between water-resistant and waterproof watches? 

Water-resistant watches can handle pressure underwater while waterproof means it should be impenetrable to water. 

Using my extensive horological background, I will break down precisely what defines water resistance and waterproof and provide tips on how to protect your coveted baby.

Is Water-Resistant The Same As Waterproof Watches?

Listen people, nothing is a guarantee...aside from taxes perhaps. That’s also evident regarding waterproof vs water-resistant watches. 

No timepiece is fully water-repellent including models such as the Rolex Sea Dweller and Rolex Oyster. Since 1926, first rate performance and durable water-repellent properties has seen these reliable divers plunge to at least 100 meters. 

Only two watches, the iconic Rolex Deep Sea Special and Rolex Sea Dweller Deepsea have ever reached the deepest part of the ocean, some 11,000 meters under the surface. The Sea Dweller Deepsea can withstand mammoth depths up to a staggering 13,000 meters. Nevertheless, it’s not fully marked as waterproof. 

The bottom line watch fiends are that no timepiece is completely impervious; rather there are models that can deal with substantially more water damage compared to other watches. 

Meanwhile, the number of ISO 6425 tests conducted in workshops test how water resistant a dive watch actually is before it is deemed a genuine “diver” of at least 100 meters.

Meeting various criteria including a condensation test, checking pressure resistance and immersion will only ensure IS0 6425 status. The watch is also subjected to a tremendous amount of external force and then assessed for any water leakages. 

A man wearing a silver round analog watch

How Does the Weather Affect Water Resistance?

When it comes to everyday usage, active submersion or exposure to liquids i.e. light rain or hot showers is risky and may cause repeated damage. This is down to regularly changing air and differing temperature fluctuations. 

In warm weather, this can prove to be a genuine problem for watches as certain components can expand. Continual wet conditions or exposing the watch to light showers can penetrate through, leading certain gaskets and seals to corrode. 

What Is Water Resistance?

In watch circles, this is classified by how much water pressure a watch can withstand. ATMs, known as atmospheres or meters is the designated unit that records how water resistant your watch is.

This ranges from 1 ATM or 10 meters all the way up to 20 ATM (200 meters) and even 30 ATM (300 meters) like the highly regarded Omega Seamaster Diver Watch. 

Mind you, diver watches are only based on water resistance up to a certain degree as there is a possibility that moisture damage could seep into the movement or case. 

A watch might state 200m or 300m but this is run through a series of strenuous tests undertaken by dedicated time lords in the lab as we have mentioned under a number of different scenarios.

Among other areas, this involves the overpressure test, examining crown resistance, and even having a swimmer sit at a particular depth in the water. 

Can I Swim with a Water-Resistant Watch?

Any sudden body movements like swimming energetically or taking your timepiece within proximity of the depth rating could affect overall performance. Whether hitting the beach, taking a dip in the ocean, or windsurfing with chums, it’s advisable not to take your watch near the given rating.

Furthermore, there are several factors that can affect how water-resistant a watch is. From close contact with steam and hand washing to scoring at water polo, this can all play a pivotal role in the force exerted. 

Therefore, you'll need to have your watch checked every two years ideally. This should ensure your timepiece stays in tip top condition and the seals are in working order. 

Person swimming on body of water

How Are Water-Resistant Watches Rated?

Now that you ask, let’s put you in the picture. 

Water Repellency

Water repellency is rated via two methods. Tested in meters, this is either firstly branded on the case or caseback as an uppercase “M” or lowercase “m”. 

Secondly, atmospheres or ATM is the specification as to how many meters or feet a watch can be immersed in water without any underlying damage. Normally, 1 atmosphere amounts to 10 meters of water protection. So 20 ATM is equivalent to 200 meters. 

Depending on the rating, watches can be used in a myriad of ways like splashing in the tub, shallow diving, mixed gas diving, and SAT diving. Finally, a water-repellent reading can be expressed as “Bar”. 

A common occurrence which features across Europe, this unit measures the level of water repellency instead of depth. Although you won’t find it readily available on a dial, 1 bar is the same as 1 ATM. Always check the water repellency rating before taking the plunge. 

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Tick Tock...The Final Word

As we have learned in this article, waterproof essentially signifies something which is impenetrable to moisture without any leakage. When it comes to watches, this isn’t a cast iron guarantee and hasn't been used by the Federal Trade Commission for half a century. 

In its place, “water-resistant” has now appeared on the horological scene, making its mark thanks to ISO 6425 and ISO 2281 standards. 

Testing both divers and water-resistant watches respectively, a fully waterproof watch that can repel water does not exist. Rather it is characterized by a water resistance rating. The Rolex Oyster series is really as good as it gets.  

What’s our advice? Make sure you purchase a watch offering a minimum 10 ATM rating. Oh and don’t forget a locking crown and waterproof straps for a soggy-free experience. 

Simon Lazarus
As an avid watch fiend, Simon Lazarus isn’t any ordinary watch collector. Since the dawn of time (well almost), his obsession with timepieces has seen him establish a bijou collection across his extensive travels with his wife and two darling daughters including in the US and Dubai. With an extensive back catalogue of published work on timepieces for numerous sites globally, watches are moments in history. He certainly makes time to capture the true essence of watchmaking with an eye for impeccable detail showcased in his plethora of watch articles across numerous sites. With a well formed selection focusing on Swiss made as well as emerging microbrands that will no doubt gain in value, time is almost as precious as his two young princesses!
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