Understanding Watch Water Resistance: Depth Ratings, ISO Standards & More
Watches today are more than just time-telling tools—they’re everyday companions built for everything from daily wear to swimming, diving, and rugged outdoor use. If you’re in the market for a durable timepiece or want to care properly for the one you already own, understanding watch water resistance is essential.
In this guide, we’ll explore what water resistance really means, how it’s measured, the testing methods manufacturers use, and the official standards that define whether your watch can truly withstand water exposure.
The History Behind Water-Resistant Watches
Water resistance in watches has evolved in tandem with advancements in watchmaking and outdoor activities. The quest for watches that could withstand water exposure began in the early 20th century when wristwatches became more popular and practical for active lifestyles.
Early Innovations:
1920s-1930s: The first attempts to make watches water-resistant focused on improving the case design and sealing mechanisms. Early watches had simple rubber gaskets and screw-down case backs to prevent water from entering.
Rolex Oyster (1926): A landmark moment in watch history came with Rolex’s introduction of the Oyster case. It was the first truly water-resistant wristwatch, featuring a screw-down crown, case back, and bezel. The Oyster case was famously tested when Mercedes Gleitze swam across the English Channel wearing the watch, proving its water-tightness.
Development of Diving Watches:
1950s: As scuba diving gained popularity, watchmakers began designing specialised dive watches capable of handling greater depths and pressures. Brands like Blancpain, Rolex, and Omega pioneered models with increased water resistance and legibility underwater.
ISO 6425 Standard (1982): To unify the criteria for diving watches, the International Organisation for Standardisation (ISO) released the ISO 6425 standard, outlining rigorous testing requirements for water resistance, shock resistance, visibility, and other key features.
Modern Advances:
Today, watches offer water resistance ratings from everyday splash-proof models to professional dive watches capable of withstanding pressures equivalent to depths of 1000 meters or more. Innovations in materials, gaskets, and case construction continue to improve reliability and durability.
Understanding Watch Water Resistance: Ratings, Depths & Limits
Water resistance refers to a watch's ability to resist water ingress under specific conditions. Contrary to popular belief, a water resistance rating does not mean a watch can be submerged to that exact depth indefinitely. Instead, it represents the maximum pressure the watch can withstand in a controlled testing environment.
Water resistance ratings are most commonly displayed in:
Meters (m)
ATM (atmospheres)
Bar (1 bar = 1 ATM = 10 meters)
Common Water Resistance Ratings:
| Rating | Meaning | Suitable Activities |
|---|---|---|
| 30m / 3 ATM | Splash resistant | Handwashing, rain |
| 50m / 5 ATM | Light water exposure | Showering, light swimming |
| 100m / 10 ATM | Good for swimming | Swimming, snorkelling |
| 200m / 20 ATM | Diving-level resistance | Recreational scuba diving |
| 300m+ | Professional-grade diving | Deep diving, marine sports |
How Is Water Resistance Tested?
Watch manufacturers perform rigorous water resistance tests to simulate real-life scenarios and pressure conditions. These tests ensure the timepiece can withstand the water pressure indicated on its dial or case back.
Key Watch Water Resistance Tests:
Water Pressure Test: Simulates increased pressure to confirm resistance to depth.
Condensation Test: Detects internal moisture when the watch is heated and then cooled.
Thermal Shock Test: This test measures resistance to rapid temperature changes, a common challenge when transitioning between environments (such as hot tubs and cold pools).
How to Maintain Your Watch’s Water Resistance
The water resistance of your wristwatch is not permanent—it degrades over time. Here’s how to keep your watch water-resistant:
Regular servicing: Get your watch pressure-tested and gaskets replaced every 1–2 years, especially if you swim regularly.
Avoid hot water: Steam from hot showers or jacuzzis can damage seals.
Rinse after saltwater exposure: Saltwater can corrode metal parts and affect water resistance.
Check the crown: Ensure it’s always pushed in or screwed down before exposing the watch to water.
Choosing the Right Water-Resistant Watch
Understanding water resistance helps you choose the right timepiece for your lifestyle. Whether you're looking for a casual water-resistant watch for everyday use or a professional dive watch, it's essential to:
Know what the water resistance rating actually means.
Confirm it’s been adequately tested.
Maintain regular inspections to ensure the watertight integrity is preserved.
By staying informed about water resistance levels, testing methods, and industry certifications, you’ll protect your investment and enjoy worry-free performance in any environment.
Does Pressure Testing Guarantee My Watch Is Waterproof?
No, pressure testing does not guarantee that your watch is completely waterproof. Instead, it verifies that your watch meets its specified water resistance rating under controlled conditions. Water resistance refers to the watch's ability to withstand specific depths or pressures without water entering the case. However, real-life factors such as temperature changes, ageing seals, and impacts can affect its performance. So, while pressure testing confirms the watch’s current water resistance, it doesn’t make the watch invincible to all water exposure.
What Do You Do When Water Gets Into Your Watch?
If water gets into your watch, here’s what you should do immediately:
Stop wearing it: Remove the watch right away to prevent further damage.
Avoid shaking or pressing buttons: This can cause water to be pushed deeper inside.
Dry the exterior: Gently wipe the outside with a soft cloth—don’t try to open the watch yourself.
Get professional help ASAP: Take your watch to a trusted watch repair specialist immediately. They can open the case, dry the internal components, clean or replace parts if needed, and reseal your watch to restore water resistance.
Don’t delay: The longer water stays inside, the higher the risk of corrosion and damage to the movement.
Quick action is key to saving your watch when water gets inside!
Protect Your Wristwatch with Our Certified Watch Pressure Testing
At AMJ Watch Repair, we offer professional pressure testing, seal replacement, and expert watch repairs to keep your timepiece in top condition. Contact us today to book a service or visit our watch repair workshop shop in person, located in the heart of London's historic jewellery district, Hatton Garden.
