Water Resistance in Watches: The Complete WR Rating Guide

At Joyería Sendra, we want to help you get to know and understand watches in a way that's both professional and approachable. That's why we're bringing you a series of blog posts to help answer your questions and teach you a little more about these beautiful precision timekeeping instruments.

This time, we're tackling a topic that can be a bit confusing for those just starting out in the watch world: water resistance.

Let's start by talking about the terminology.

The water resistance rating can vary between brands. Typically, and most commonly, this rating is given in meters (m), feet (ft), atmospheres (atm), or bar. The pressure exerted by a 10m column of water is roughly equivalent to 33ft, 1atm, or 1bar.

There are two fundamental types of water resistance:

1. "Water Resistant" classification: this label applies to devices that meet the ISO 2281 water resistance standard. It's based on synthetic or artificial pressure tests carried out in a hyperbaric chamber (though these are usually vacuum chambers — keep in mind this pressure testing is only for the purposes of certification. Your watch isn't actually "pressurized" in daily use; that would be catastrophic).
2. "Diver's" classification (or diving watch): this label applies to devices that meet the ISO 6425 water resistance standard for diving instruments. It's based on synthetic or artificial pressure tests in a hyperbaric chamber, as well as real-world testing at a depth 25% greater than the stated rating.

The difference is clear. While a watch rated WR 50m or higher is guaranteed for use with water (30m if it's Swiss Made or from a reputable brand, like all the ones we offer here), a diving watch must specifically be a DIVER's-rated watch. Selling a WR 100m watch as a diving watch — where, remember, your life could be at stake — is a serious mistake. That said, results can vary by brand: Casio G-SHOCK models, for instance, with their 200m water resistance, are commonly used underwater by tens of thousands of "casual" divers thanks to their solid reputation.

Let's get into the details:

NOT GUARANTEED FOR WATER USE:

• WR 1m (1atm or 1bar): While, as noted above, 10m corresponds to 1atm, here we see 1m = 1atm = 1bar. This type of watch is NOT WATER RESISTANT AT ALL. It simply means the watch can withstand normal atmospheric pressure — in other words, even air humidity can get in. This is the typical rating you'll find on the cheap "made in Asia" watches sold in newspaper promotions and bazaars.
• WR (ISO 2281): This rating is similar to the previous one, but comes from a more serious manufacturer that isn't trying to mislead you (even though the terminology itself, due to technicalities, can be a bit confusing). Watches with this label are NOT WATER RESISTANT, but they do offer some protection for normal use, such as washing your hands with a bit of caution. Water shouldn't run directly onto the watch, but it should tolerate incidental contact. Keep in mind there's a difference between a WR rating on a CASIO RETRO and one on, say, a MAREA (to name a commercial brand). CASIO watches are used heavily by their owners, and warranty claims for water damage are rare. Either way, understand that this isn't a guarantee — we're simply sharing real-world results so you can understand the difference between a solid manufacturer and a "fashion brand."
• WR 30m (3atm, 3bar) (ISO 2281): This rating protects against everyday use. Even though we shower daily, "everyday use" here means normal use with accidental water contact, like washing your hands — not sustained, deliberate exposure such as showering or bathing. This rating is usually not covered under the manufacturer's warranty for water damage.

GUARANTEED FOR WATER USE:

To reiterate: if a watch is rated for water use, then unless there's clear evidence of major damage, unauthorized tampering by a third-party repair service, or the watch has been fully flooded, the manufacturer has no real way of knowing whether you've used the watch beyond its rated limits — so the warranty should cover these issues. In any case, at Joyería Sendra we do our best to give you the information you need to take care of your watch so it lasts many years in perfect condition. Give it proper use and the maintenance it deserves, and you'll end up with a loyal companion you can rely on.

• WR 50m (5atm, 5bar) (ISO 2281): This rating is designed for normal daily use, including showering and regular surface bathing. "Normal bathing" here means swimming in the sea or a pool, but not intense water sports, such as diving into a pool or activities like jet skiing. Saunas and very hot showers aren't recommended either, and in general, sudden temperature changes are quite risky. This water resistance level is suitable for most users, most of the time.
• WR 100m (10atm, 10bar) (ISO 2281): This rating is designed for those who want to stop worrying about how they use their watch day to day, since these watches offer strong water resistance. This is our minimum recommendation for active users, as there are plenty of WR 100m watches available at very accessible prices, such as the Edifice EF-125D-2AVEF. Although not designed for it, you'll often find brands and retailers claiming these watches are fine for freediving or snorkeling. In reality, they're intended for normal use in popular surface water sports, such as water polo, swimming, or jumping into the water from a pool edge or low height. Using terms like "scuba diving" or "diving" can be misleading, but as we've tried to explain, moderate water sports are perfectly fine. These watches are also less vulnerable to sudden temperature changes, though if the watch has been sitting in direct sunlight and is hot, you shouldn't expose it to the thermal shock of cold water.
• WR 200m (20atm, 20bar) (ISO 2281): This rating is designed for watches with intensive water use, such as surface diving, snorkeling, and more extreme water sports like rafting or jet skiing. These are, therefore, highly water-resistant watches with very robust cases.

GUARANTEED FOR DIVING USE:

WR 100m and WR 200m watches are great, but... what happens when your life is actually on the line? For many professional divers, using a dive computer is mandatory, but even a dive computer can fall short when your own life or someone else's is at risk — which is why professional divers and diving instructors often carry up to two timekeeping tools for redundancy. This brings us to two distinct use cases for DIVER's watches: professional divers who use a dive computer and want a second, reliable tool in the form of a proper diver's-rated watch, and experienced non-professional divers who want a quality tool they can also wear outside the water as an everyday watch or fashion accessory.

These users are the reason watches meeting the ISO 6425 standard exist. According to this standard, a compliant watch must include the following features:

1. A way to visually track elapsed time without relying on complex cognitive skills (like memory), for situations involving mild dizziness or disorientation. This takes the form of a rotating bezel (typically unidirectional, to prevent accidents).
2. A screw-down crown and pushers (which should not be operable mid-dive), to protect them from accidental activation.
3. A dial and hands/markers with luminous coating for easy readability in low-light or low-visibility conditions.
4. An anti-reflective crystal, to further improve visibility.
5. The ability to withstand a depth 25% greater than the stated rating (verified through real-world testing, though note this isn't tested on every individual unit)

DIVER's watches span a wide range of water resistance ratings, from DIVER's 150m (now largely discontinued, found on more classic models) up to DIVER's 5000m for some extreme models. That said, the most popular ratings tend to be the ones below — all of them extremely well suited to any type of diving, including extreme dives carried out by highly experienced professionals using specialized equipment:

• Diver's 200m (20 atm, 20bar)(ISO 6425)
• Diver's 300m (30 atm, 30bar)(ISO 6425)
• Extreme Diver's watches with a helium escape valve for saturation diving (ISO 6425): Some DIVER's-rated watches come equipped with a helium valve (nowadays typically automatic) for saturation diving. Helium is an extremely "fine" gas that can seep inside a watch case under very high pressure and low temperatures, well before water would be able to do the same. Helium also builds up inside the watch during saturation diving, when divers spend time in a hyperbaric chamber. That's why these watches feature an ultra-fine valve that lets the gas escape as pressure in the chamber normalizes, or as the diver ascends. For the vast majority of users, this feature isn't strictly necessary, but many of us simply enjoy owning these technical marvels, even without any plans to use them anytime soon.

Additional considerations:

The meter ratings used to indicate a watch's water resistance come from lab tests carried out with the watch at room temperature on a pressure-testing machine, usually without water (older testing methods used water; more modern, reliable machines apply both negative and positive pressure and measure crystal curvature as a reference for how much deformation the watch can withstand without "absorbing" or "leaking" air). When you're actually wearing the watch, it's exposed to ambient temperature, which can rise further under direct sunlight — and this thermal effect acts as a "multiplier" on pressure. On top of that, movement in the water and/or currents (such as the pressure from a tap's water jet) create another "multiplier" effect on that pressure. Because of this, relative pressures at the surface can sometimes exceed what the watch is actually rated to withstand. Lab conditions are difficult to replicate in everyday life, though they remain useful for study and understanding.

Beyond these considerations, there are a few additional recommendations to help you get the most out of your watch.

• If your watch has a leather strap, even if the watch itself is water-resistant, we recommend avoiding water exposure, since leather straps deteriorate much faster when wet.
• If you swim in the sea, it's a good idea to rinse your watch with fresh water as soon as possible to remove any salt residue. The same applies after swimming in a pool, to rinse off chlorine residue.
• Every time a watch is opened — for a battery change, for example — it loses its water resistance. This happens because the gaskets are placed under pressure once the case is sealed. Once opened, if the gaskets aren't in perfect condition, they won't return to their original state. That's why, whenever a watch needs to be opened for servicing, the following steps should be carried out:

1. Clean the case of any dirt or debris
2. Clean the crown tube and pushers
3. Replace the gaskets on the crown, pushers, case back, and crystal
4. Lubricate the gaskets with silicone grease to ensure a proper seal
5. Properly reseal the watch case
6. Run a water-resistance (pressure) test to confirm the replaced gaskets are performing correctly

It's true that if the gaskets are in perfect condition, running the test alone may be enough. But it's also true that even if they're fine today, they might not be in a few months — and new gaskets are the best guarantee of lasting performance. That's why, if you truly care about your watch, it's essential to replace the gaskets and carry out the complete service; especially considering that, relative to the cost of the job, gaskets themselves are very inexpensive. We recommend going to a specialized service center that guarantees its work for at least one year. And remember, at Joyería Sendra we guarantee all our repairs for 2 years, just like the top names in the industry. That's possible because we're an AUTHORIZED service center for a great many brands, so we apply the same standards across the board — whether a brand requires it of us as their authorized service center or not. Cutting corners for some brands and not others just isn't how we work. And if water resistance can't be guaranteed based on the test results, we don't charge for the extra service, and we make sure to share all the relevant information with the customer.

For example, if a battery change and water-resistance service is needed on a water-resistant watch, we carry out the entire process described above. If the test comes back negative, we repeat it, even more thoroughly this time, replacing any gaskets that could be faulty (worth noting, this happens in fewer than 1 out of every 500 services). If it happens again, it means there's a defect in the watch case itself. We then assess the situation, and it may turn out that the crown, crown tube, or crystal gaskets need replacing... in which case we issue a new quote. This new quote doesn't re-charge for the work already done — it's priced as if the full job had been identified from the start. And if the customer declines, they'll get their watch back with a new battery and new gaskets for the price of a standard battery change, understanding that the watch is no longer water-resistant, or at least that this can no longer be guaranteed. Information, service, warranty, and the best possible price for the best possible work — that's the guarantee at Joyería Sendra.