It says "100m W.R." on your watch dial. And perhaps "10 ATM" on the watch’s caseback. You already know it refers to the watch’s maximum water resistance but is there more to it than those mere numbers?
If you have a 100m rated watch, would you wear it for scuba diving?
Well, why shouldn’t you? After all, the manufacturer labeled your watch as "100m water resist" and and you’re not likely to venture any deeper than 50 meters into the briny blue, so why not?
Perhaps your watch "looks like the very ones that you see professional divers wear on the National Geographic or Discovery Channel so you start thinking you could take your watch on your next diving trip too!
Then, you consult your watch owner’s manual and you get a shock. You learn that the manual states that your 100m rated watch is good for hand washing, showering and pool swimming only.
Sounds confusing? Why is a 100m rated watch good only for swimming and snorkeling only? What does the water resistance rating actually mean? Heck, I was once just as confused too! 🙂
The Basics of Water Resistance
Firstly, we need to understand that a manufacturer’s water resistance ratings for general watches are usually based on sterile, laboratory testing. They don’t really use real world conditions to test their products.
Generally, the resistance resistance properties of a watch is based on the following criteria:
The construction of the watch case
Design and condition of the rubber "O-ring" seals and gaskets
Thickness and hardness of the watch glass or crystal
Crown and push button design
Construction of the watch case
Generally, thicker cased watches are often employed for timepieces that are rated to 100m W.R. (Water Resistance) and above. The thicker the case, the stronger it can withstand crushing pressures in the deep. Some professional dive watches that have a rating of 600m usually made from titanium as it is lighter and stronger than stainless steel.
In the same vein, dress watches are not meant to be immersed in water, let alone worn for recreational or scuba diving. Dress watches are generally slim and their water resistance is usually limited to 50 meters or less. Although the manufacturer may state 50m W.R. rating, it doesn’t mean that you can take the watch to 50 meters in the water. At best, you can wear your watch in a swimming pool and that’s just about it.
At the other end of the spectrum, professional dive watches are often bulky and bulbous in design. Some have shrouds (like the Prospex SBBN011 1000m) to help fortify the watch case and also protects the case against accidental knocks and scrapes.
Seiko’s three famous 1000m shrouded Professional divers in chronological order of production: the discontinued S23517J, SSBB018 and the currently sold SBBN011 “Darth Tuna"
Other professional dive watches have taken a different approach. For instance, Sinn Hydro UX diver has a slimmer case than any of Seiko’s Professional 1000m divers.
Instead of increasing the thickness of the watch case, the Sinn UX is a silicone oil-filled watch to reinforce the watch’s structural integrity. Oil is virtually impossible to compress and strengthens the watch against extreme water pressure. In addition, the clear silicone oil filled dial assists in reading the time due to water refraction and reflection.
Above: The oil-filled quartz Sinn Hydro UX (left) and the UX GSG-9 military issue model from its 2007 lineup
Since automatic movements can’t function in a viscous medium such as oil, Sinn used a high torque quartz movement instead. Silicone oil is an inert substance, it’s non-conducting and non-corrosive. You can see from the top right photo that the dial is quite readable from extremely flat angles.
The catch is that since the UX is a quartz watch, its battery will inevitably need to be replaced. As far as I know, owners will have to send the watch Sinn’s factory in Germany as the silicone oil has to be drained out before replacing the battery. The oil is then refilled and checked prior to shipping it back to the owner. That’s probably the most expensive battery change job I’ve ever heard in my life! 😉
Design and condition of the rubber O-ring seals and gaskets
All water resistant watches have rubber seals (whether natural rubber or synthetic) to keep out dust, moisture and of course, water. Higher W.R. watches tend to have thicker and more robust caseback gaskets made of higher quality rubber. Unfortunately these rubber seals don’t have an infinite life span. Rubber eventually hardens over time and will eventually develop cracks which will compromise your watch’s resistance to water.
If you have a diver’s watch that’s over 10 years old, it’s usually recommended to have all the gaskets and seals completely replaced. Like alternator and air-condition belts in automobile engines, rubber will eventually deteriorate and lose their sealing properties.
Although Seiko advocates annual checking or replacement of its watch seals, I personally don’t think it’s necessary unless you swim with your watch on a frequent basis. If you have a quartz watch, it may be a good idea to replace the gaskets on your next battery change, assuming the watch’s battery can run for 5 years or longer. For mechanical watches, you might want to have the seals changed when you take your watch for a periodical service – maybe once in six years.
Chemicals like chlorine, soap and detergents (e.g. taking a shower with your watch on) also help to hasten deterioration of the rubber material. Therefore if your watch always accompanies you into the swimming pool, you might want to have the seals checked by your watchmaker or authorized repair center annually.
Thickness and hardness of the watch glass or crystal
Timepieces that are designed for scuba diving have thicker crystals to withstand water pressure compared to dress watches. The choice of crystal material, whether its made of mineral glass (Seiko calls their glass Hardlex), Sapphlex (Hardlex glass with a top sapphire laminate) and true sapphire crystals doesn’t influence a watch’s resistance to water pressure. Its thickness however, does.
Watches that are traditionally equipped with acrylic crystals, like some vintage watches such as the Seiko 4006/4005 Bell-Matic and the original Omega Speedmaster are not meant to be taken to swimming excursions, let alone taken along for diving.
Although Seiko’s first true dive watch – the 6217 or "62MAS" was also equipped with an acrylic crystal, the crystal itself had to be extra thick to withstand 150 feet of water pressure.
Acrylic crystals may not be as reliable as glass under pressure. In fact, Seiko’s second generation diver – the 6105-8000 model marked the manufacturer’s move from acrylic to mineral glass. From then on, all Seiko dive watches have crystals that are made from mineral glass or sapphire.
Seiko’s first diver, the acrylic crystal-equipped 6217-8001 (left) and its successor, the 6105-8000 (right)
Crown and push button design
All diver’s watches have screw-in crowns and seals for water-tightness. As long as the crown is screwed into the case snugly, the watch is water resistant to its indicated depth. Some sports watches also have screw-in crowns but they are not intended for scuba diving.
Very few diver’s watches have buttons or pushers that are designed to be operated underwater. These are usually models that have depth gauge sensors like the wrist dive computers that modern day divers wear. Seiko’s digital NX-series and its analog SLD005J have buttons that can be pressed underwater. Citizen also produces several Promaster Aqualand divers with depth gauges that can be operated while submerged. The buttons are specially constructed with seals that keep the water out when pushed in.
Such dive watches are usually costly and those who buy such timepieces are usually people (like certified PADI dive instructors) who actually go scuba diving on a regular basis.
Specialized dive watches such as the above allow underwater button operations. From left to right: Seiko NX-series, SBDK001, SLD005J and the Citizen 20th Anniversary Aqualand JV0020-04E.
Seiko also makes ISO-certified diving watches with buttons, such as the SBDQ001/003 and SNDA13/15P chronographs and several Kinetic divers with power reserve indicator buttons (the 5M-caliber series). These buttons are however, not designed to be operated when submerged. Doing so will allow some water into the case and perhaps flood the watch, damaging the movement.
For this reason, Seiko’s owner manual explicitly states "Do not operate the buttons when the watch is wet for their non-professional diver’s watches.
These ISO-certified Seiko divers should not have their buttons depressed while underwater: the SBDQ003 and SNDA13P quartz chronograph divers and the yellow SKA376P Kinetic diver.
How watches are tested for water resistance
Watch manufacturers’ water resistance ratings are based on sterile laboratory testing. Generally non-diver’s watches are subjected to static dry pressure tests, which involves placing watches into a dry pressure chamber. Pressurized air is then pumped into the chamber up to the intended pressure to simulate depth in water.
Should the watch have a leak, the case will slightly expand which means that the watch allowed some air into the case, hence failing the pressure test. Either the rubber seals didn’t hold up to the pressure or the watch glass wasn’t fitted properly.
Above: A wet chamber pressure tester. Photo courtesy of Kineticrepair.com
The manufacturer can also use the wet pressure testing method, which involves pumping pressurized air into the watch in a chamber. The watch is then immersed in water. If there’s a leak, bubbles will escape from the watch. failing the water resistance test.
The timepiece is then inspected and rectified or even discarded as a defective unit, depending on the manufacturer’s quality control policy.
Here’s an excerpt from Wikipedia, relating how standard watches are tested for water resistance:
ISO 2281 water resistance testing of a watch consists of:
- Immersion of the watch in 10 cm of water for 1 hour.
- 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.
- Immersion of the watch in 10 cm of water at the following temperatures for 5 minutes each, 40°C, 20°C and 40°C again, with the transition between temperatures not to exceed 5 minutes. No evidence of water intrusion or condensation is allowed.
- Immersion of the watch in a suitable pressure vessel and subjecting it to the rated pressure for 1 hour. No evidence of water intrusion or condensation is allowed.
- Exposing the watch to an overpressure of 2 bar, no more than 50µg/min of air is allowed to get inside the case.
- No magnetic or shock resistance properties are required.
- No negative pressure test is required.
- No strap attachment test is required.
- No corrosion test is required.
In practice, the survivability of the watch will depend not only on the water depth, but also on the age of the sealing material, past damage, temperature, and additional mechanical stresses.
None of the tests defined by ISO 2281 are suitable to qualify a watch for scuba diving. Such watches are designed for everyday life and must be water resistant during exercises such as swimming. They can be worn in different temperature and pressure conditions but are under no circumstances designed for diving with underwater breathing apparatus.
The water resistance table
Let’s take this water resistance chart that Seiko prints on its website and learn to interpret what the chart describes.
Seiko’s Water Resistance Chart
As you can see from the chart above, it states that if the marking on the case says "5 BAR" (translation: 1 Bar = 10 meters, so 5 Bar = 50 meters) the watch could only be taken for "swimming, yachting and taking a shower". So how come bathing and shallow diving is not permissible? Your bathtub is surely no more than 1.5 meters deep. And your average swimming pool couldn’t even be twenty meters deep, could it? 😉
Watch manufacturers usually furnish water resistance capabilities conservatively. They base their recommendations on the fact that you’d want your watch to last as long as possible. Compare the 20 Bar entry against the Diver’s watch 200 meters. According to the table, 20 Bar rated watches are good up to "bathing and shallow diving" while the Diver’s watch is permissible for scuba diving.
Can a 50 meter W.R. watch taken down to 50 meters underwater?
Theoretically, you can. If the rubber seals are fairly new, your watch has a good chance of surviving to 50 meters in water. But then we have to remember that non-diver’s watches are tested in lab conditions using static pressures, which do not exist in real world situations.
In the depths of a body of water, undercurrents exist. The act of swimming against water and currents also create dynamic pressure, which is exerted upon the watch that you’re wearing. Therefore at just thirty meters beneath the ocean, the water pressure that you and your watch can be a lot more than 5 Bars, which goes past the manufacturer’s water resistance rating.
Even a simple act like jumping off a high diving board into a swimming pool can result in a pressure which exceeds the watch’s design limitations. You may end up with a deformed watch case or a cracked crystal due to the impact. Which can lead to water intrusion and damage to your timepiece.
A rough-but-simple analogy would be comparing a sports car with an economical sedan for daily commuting. It’s fairly easy for a normally aspirated 1.5 liter Honda Civic to be driven at 180 kilometers an hour on a long, flat road. Sure, if you’re the only one in the car with no luggage load and given the right conditions like no headwind and a with the assistance of a slight downhill gradient, you might be able to hit even 200 km/h. 😉
However, if you drive the Civic like this too often you’re actually exceeding the car’s intended design – and at 200 km/h your engine revs would be hovering on the tachometer’s redline. Keep this up frequently, sooner or later your engine will wear out quickly. It’s just that the Civic’s small engine wasn’t designed to be driven frequently at that speed in the first place.
In contrast, a Chevrolet Corvette sports car with a big engine block could easily attain the same speed without even breaking a sweat. Its huge engine power and torque enables it to cruise at 200 km/h effortlessly with the engine ticking over at a leisurely pace. Obviously the Corvette was designed for reliable, sustained high speed driving whereas the 1.5 liter Civic was not.
The two famous "C"s – the Corvette and the Civic. One was made for pure speed, the other for fuel economy (illustration purposes only)
Similarly, you could take your 50-meter W.R. rated watch to fifty meters underwater but if you do it too frequently, you’re risking your watch’s water resistant integrity. You’ll be stretching your watch’s water resistance limits to the max. For this reason watch companies make watches that are specifically designed for recreational and deep sea diving.
Is a 200m sports watch the same as a 200m diver’s watch?
The short answer is NO. Although both watches are rated to 200 meters. there is a not-so-obvious difference between the two.
Although both watches have the same water resistance rating, a diver’s watch is constructed to withstand water pressure reliably at the indicated depth plus some 10-15% overhead for an extra measure of safety and reliability. Unlike an ordinary 200m sports watch, a 200m diver’s watch is designed to be survive high stresses in the long term.
Additionally, a diver’s watch also has to meet several criteria before it could be certified as a diver’s watch. When watch manufacturers design a diver’s watch, they have to meet the International Standards Organization (ISO 6426) requirements.
The criteria for an ISO 6426 diver’s watch include the following:
A minimum of 100m (330ft) depth rating
A watch case with the ability to resist corrosion from sea water, dust, shock and magnetism
An easy-to-read, legible dial with distinguishing hour markers for 12, 3, 6 and 9 o’clock
Differently shaped luminous hour, minute and second hands
A luminous dial for reading the time in darkness
An elapsed time recorder such as a timer, stopwatch or unidirectional rotating bezel
A water-resistant, screw-in crown
- An end of life (EOL) battery indicator for quartz watches (second hand ticks erratically to indicate the need to replace the cell). Mechanical divers need to be sufficiently wound before diving while Seiko’s Kinetic divers have a push button or a real-time power reserve gauge to indicate the reserve of their internal storage cell.
Although the Citizen Mission Antarctica (right) has bright luminous dial and hands, it does not qualify as a true diver’s watch like the vintage Seiko 7549-7010 Professional 300m (left).
You may have noticed that all true diver’s watches have a lumed "ball" either at the tip or at the opposite end of the second hand. The placement of the lumed ball doesn’t really matter as the primary function of the second hand is to let the wearer know that the watch hasn’t stopped working underwater.
Recreational and professional divers don’t really need precise timing up to the nearest second. For this reason, most analog quartz divers’s watches have no need for a stopwatch. The rotating bezel on these watches is sufficient to indicate the elapsed diving time up to the nearest minute.
A 200m sports watch may look like a real diver’s watch but it does not comply with the ISO 6426 standard requirements.Therefore, there is the element of risk if you wear a 200m sports watch instead of a true diver’s watch for long term diving activities.
Although both Seiko Atlas models are rated to 200m with screw-in crowns, neither are true diver’s watches.
Actually, there’s nothing really wrong wearing a sports watch for scuba diving. Some people have claimed to have no problems wearing their 100m W.R. watches for shallow scuba diving but they’re actually risking their timepieces in the long term. If you’re lucky, your non-diver’s watch can last for years without damage. In other words, your mileage may vary.
Watch companies make diver’s models for a reason – it’s not just to make profit but to ensure that they offer reliable timepieces that are designed specifically for the job.
What happens when water enters your watch?
In the case of a flooded mechanical watch, the damage to the movement can be contained if the watch is taken for repair as quickly as possible before rust sets in.
Since an automatic watch movement is largely made of plastic, brass and steel parts, the parts can be disassembled, rinsed carefully, dried, re-oiled and re-assembled. However, if the dial and hands have also gotten wet, they need to be replaced.
With non-mechanical timepieces, including quartz, Kinetic, Spring Drive and solar powered movements, the damage is usually irreversible. This is because microelectronic components constitute part of the internal movement and the components are likely to have shorted out beyond repair.
Most quartz modules use surface mounted semiconductors like any other electronic device. The only recourse is a complete movement/module replacement – assuming the watch parts are still available from the manufacturer. If it’s a vintage quartz model, you’re out of luck. 🙁
Watches that you should never take for a swim
As a general rule, any watch that do not have "water resistant" markings or with no indication of the W.R. depth should never be worn for a swim. Usually thin dress watches aren’t water resistant unless the manufacturer states the degree of water resistance.
Then again, if your watch originally came with a leather strap you definitely won’t want to expose it to water. 😉
Here’s my personal list of watches that you shouldn’t risk taking into the water:
Any Seiko watch that does not say "water resistant" on the dial or the caseback.
Any Seiko watch that has the "water resistant" text but no indication of its depth rating. These are good up to 30 meters but Seiko only indicates the depth rating for their 50m models and higher.
Rare, vintage watches that you really care about.
Any diver’s watch with gaskets and seals that have not been replaced for several years and has not undergone a recent pressure test.
Early Tissot T-Touch multifunction watches (except the new T-Touch Expert)
Better keep these on dry land: A basic Seiko 5 (30m) and a vintage 6139-6000 chronograph (70m)
Umm, I thought it was worth mentioning the Tissot T-Touch. 🙂
The Tissot T-Touch used to be a watch that I lusted after sometime ago, when it first came out. It’s a shame that for a multi-function watch with a digital compass, altimeter, barometer and thermometer, Tissot rated it only to 30 meters. A fine watch for hiking and mountain climbing, but taking it swimming is a no-no.
According to my watchmaker, the T-Touch has a tactile touch screen that’s too sensitive to be pressed strongly by the wearer’s finger (you’re supposed to touch the crystal gently, not jab on it!). I guess that made some sense as swimming in a pool will exert enough pressure on the crystal, possibly damaging the delicate sensors.
Recently Tissot has introduced new 100m W.R. T-Touch models, named the T-Touch Expert. Apart from the vastly improved water resistance rating, the Expert also includes a sorely needed backlight for the LCD display.
The first generation T-Touch with the green "T" logo and the 2nd generation with the red "T". With a measly 30m water resistance, neither watches are suitable timepieces for swimming.
Whether you want to take a non-diver’s watch for scuba diving or a watch with a low water resistant rating for swimming activities is entirely up to you.
I learned this the hard way when I immersed my old Seiko H557 analog digital watch (it indicated "water resistant" on the caseback) into a bucket of soapy water to get rid of the built-up gunk and to pry off the Seiko quality control sticker that had stuck on the caseback since 1984. Sure, it got the watch spick-and-span and the sticker did come off.
It wasn’t until the next day I had the battery replaced, my watchmaker pointed out to me that some water had gotten into the watch. It turned out that the damage was very minimal and the watch functioned perfectly. What a relief!
In 1998 I purchased my first Seiko analog watch – a 7T32 caliber SDWD19P and took it for a dip in a hotel’s swimming pool. It has a 50 meter W.R. rating and I thought, "what the heck, the pool is hardly 2 meters deep anyway" so I swam with it. I remembered timing my swim and pushed the buttons when it was wet.
Fortunately for me I had the presence of mind not to operate chronograph buttons while submerged and the watch is fine right till this day. 🙂
Two of my old Seikos that survived water intrusion by sheer luck: the H557 analog digital (left) and the SDWD19P (right)
From then on I make it a point to wear at least a 100m rated watch to the swimming pool or better still, my SKX007J diver. 😉