How to Choose the Right Water Resistance: Advice from a Watch Specialist. ~Is 100m Water Resistance Safe for Swimming?~
Hello.
I am Ikeda, the manager of Watch Lab, and I am incredibly sleepy because I accidentally fell asleep last night and woke up in the middle of the night.
Well, what I want to write about today is the question, "How much can you really trust a watch's 'water resistance' rating?"
I often receive inquiries from customers before and after their purchases regarding the water resistance of wristwatches, so I decided to compile this information in the hope that you will understand it well before making a purchase.
When you are choosing a wristwatch, you will always see notations like "5 bar (50m) water resistant" or "10 bar (100m) water resistant" on the spec sheet.
It is actually dangerous to take these literally.
The trap of the word "waterproof"
In fact, water resistance tests for wristwatches are conducted in a "stationary state."
For example, for a 10 bar water-resistant watch, the test checks whether it can withstand water pressure while being "gently submerged to a depth of 100m and kept perfectly still."
However, you are not standing still when you are actually using water, are you?
You might expose it to water gushing from a faucet or splash your arms around in a pool.
When this "movement" is added, the instantaneous water pressure easily exceeds the numbers on the spec sheet.
Think of it like an umbrella that can withstand 100 km/h winds; if you swing it around hard or a gust of wind hits it, the ribs might break.
This gap between the "water resistance on the spec sheet" and the "water pressure that occurs in real life" is the trap.
Water Resistance Comparison Table (JIS/ISO Standards)
Here, I have organized the "X bar (Xm) water resistance" commonly written on spec sheets to make it easier to understand what kind of scenes they can actually withstand ↓
・[Public rules for "water resistance" you should know]
The water resistance of a wristwatch is strictly defined by international standards ISO 22810 (water-resistant watches for daily use) and ISO 6425 (diver's watches), as well as the Japanese domestic standards JIS B 7021 and JIS B 7023 that comply with them.
"JIS (Japanese Industrial Standards)" and "ISO (International Organization for Standardization)" might sound like difficult terms, but in short, it is proof that it has cleared standards based on global rules.
Water resistance ratings are not just claims made at will; they are labels that come with a proper 'seal of approval'.
Is it safe to swim with a 100m water-resistant watch?
Now, for those who saw the table above and thought, 'So it's okay to swim if I have 10 bar (100m) resistance'.
From a watch store's perspective, the honest answer is, 'Theoretically it is fine, but we do not actively recommend it'.
In reality, there are almost no problems in most cases, but depending on the situation, it can lead to water ingress or malfunctions.
The blind spots here are 'aging', 'lack of verification', and 'environment'.
・Deterioration of the gasket
The rubber gasket, which is the key to water resistance and is sandwiched between the case and the movement, gradually hardens over time. Even if it could withstand 100m when new, it may harden and crack after a few years, making even 50m questionable. → We always perform a 'water resistance test' during regular inspections and battery replacements. If a gasket replacement is necessary, we will inform you along with the breakdown.
・Forgetting to close the crown
If the crown (the knob used to set the time) is pulled out before swimming, there is no way to prevent water from entering through that opening.
・Use in places with strong water pressure
Even though we say 'swimming,' you must recognize that swimming in a pool is a completely different environment for a watch than swimming in the ocean or a river. Swimming in a pool is relatively calm, so there is no problem using it without worry. However, in the ocean or rivers, unexpected water currents can occur, and you might hit hard objects like rocks; in such cases, you need to be careful even with the same water resistance rating.
Common inquiries and how to deal with them
Our store also receives many inquiries when the leisure season arrives. Let's learn the boundaries of 'what you should not do' from common cases.
① 'My watch fogged up while I was playing in the river with my children'
As mentioned in the previous section, playing in a river is actually harsher than a pool. The amount of moisture inside a watch is not zero; there are always some water molecules present. This is a case where condensation occurs in the internal air due to plunging your hand into a rapid current or being rapidly cooled by cold water.
NG: Entering a river with a watch rated at 5 bar or less.
Simple remedy: If the glass fogs up, pull out the crown (knob) and use a hair dryer set to 'cool' or 'low heat,' keeping it at least 20-30cm away. Please do not use hot air for a long time, as it will dry out the internal oil and cause malfunctions. (This is only a first-aid measure. Heat accelerates the deterioration of the gasket, so please leave it to a watch store in principle.)
Leaving it alone thinking, "It'll be fine once it dries," is the most dangerous thing you can do. If the internal mechanism rusts, it may be beyond repair, so if you are concerned, please contact your retailer.
② "The glass broke while surfing"
This is more likely due to water entering through a gap where the crown was distorted by strong force, such as hitting a board or the impact of waves, rather than "pressure difference." (The actual cause of the breakage is determined by inspection after submitting a repair request to the manufacturer.)
Seawater is several times more damaging than fresh water and will corrode the interior overnight.
NG: Marine sports with a watch that does not have a screw-down crown.
Countermeasure: There is no simple way to deal with seawater, so if seawater gets inside, wash the surface with fresh water immediately to prevent further salt from entering, and without letting it dry, contact a watch shop immediately.
※ Familiar enemies more dangerous than "water"
And, lurking in daily life, the things you should be even more careful about than water are "hot water" and "soap".
Some people think, "It's 100m water resistant, so baths and saunas are fine!" but this is an action that drastically increases the risk of failure for a watch.
The reasons are:
Thermal expansion: Metal cases and glass have different thermal expansion rates, which creates tiny gaps.
Steam intrusion: Even if it can block water droplets, "steam" with its fine particles can slip past the gaskets and get inside.
Soap/Shampoo: Surfactants reduce the surface tension of water, making it easier for water to enter through gaps that would normally repel it.
For these reasons, try to take off your watch whenever possible when in the bathroom or doing dishes.
Summary: To enjoy your watch for a long time
In reality, thinking of the water resistance of watches under 20 bar/200m as just "insurance for emergencies" is the secret to a long life with your favorite timepiece.
Most watches will be fine even if they get a little wet, but for watches you haven't worn in a while, unexpected things can lead to failure.
Daily use (3-5 bar): Water splashes while washing hands or light rain are okay.
Active (10 bar): Can withstand water play or accidental submersion.
Marine Sports (200m or more): This is the level where you can confidently head into the ocean.
Rather than overestimating by thinking "it's waterproof so it's fine," treat your watch with a little bit of care, remembering that you are wearing a precision instrument. That way, your watch will continue to keep accurate time for you.
See you next time.
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