A lot of people ask me what they need to look for in a watch for diving, surfing, rafting etc. Many say "150ft (50m) water resistance is enough isn't it? I won't be going down more than 75ft (25m)." I wish it was that simple but unfortunately its not. There are several important features that make a watch water-resistant. The most important is the gaskets, or 0 rings-which are made of rubber, nylon or Teflon, these form watertight seals at the joints where the crystal, case back and crown meet the case. if the watch is a chronograph, the chronograph pushers will also have gaskets and the more gaskets you have the greater the risk one might fail. In addition, water-resistant watch cases are lined with a sealant, applied in the form of a quick-hardening silicon liquid, which also helps keep the water out.
The thickness and material from which the case is made is also a big factor in determining whether a watch can safely be worn underwater. The case must be sturdy enough to withstand pressure without caving in. In general, this means a steel or titanium case. A screw-in case back, as opposed to one that pushes in, also contributes to a watch's water resistance. A screw-in crown, a feature of many divers' watches, helps prevent water getting into the case through the watch-stem hole. When it is screwed down it forms a water tight seal like the hatch on a submarine. Generally screw crowns are used when the watch is rated at water resistant to 100m/330ft or more.
Great care is needed to select the correct watch because I was horrified when I discovered that my Breitling Emergency was only 30m / 99ft rated which is just splashproof! I has been swimming and jet skiing with it for 8 years and as a collector how I missed this is anyones guess but luckily it never leaked and performed with exemplary reliability in every situation but nevertheless it is a really low rating for such a cutting edge watch.
Definition of Water Resistance
The various different levels of water resistance as expressed in meters, atmospheres or feet and are only theoretical. They refer to the depth at which a watch will keep out water if both the watch and the water are still. These conditions, of course, are never met in the real world. When you are swimming the movement of the wearer's arm through the water increases the pressure on the watch dramatically and this increase is even greater if you are water skiing or jet skiing; in effect this means it can't be worn to the depths indicated by lab testing machines and it is vital to select the correct watch. Personally I always opt for a minimum of 50m - the above being an exception!
Some watches are surprisingly water resistant and among them is the Marathon Chronograph below rated at 300m / 1000ft which is exceptional for a chronograph which are normally rated 50m or 100m. This is one of the mil-spec watches in my top 5.
MARATHON Chronograph with 300m / 1000ft Water Resistance
The following usage recommendations are suggested by most watch manufacturers and there is also some very detailed information here which sets out the technical standards in detail.
- Not Rated or Stated. Assume it is not water resistant at all especially if its an old watch. (we added this note because a watch arrived today from a brand we don't recognise that was brand new and divers style but when we checked it on a pressure tester it had no water resistance etc and had leaked writing it off completely)
- Water-resistant to 30 meters (100 feet/3atm). Will withstand occasional splashes of water or light rain but should not be worn while swimming or diving and all contact with water is best avoided.
- Water-tested to 50 meters (165 feet/5atm). Suitable for swimming in shallow water.
- Water-tested to 100 meters (330 feet/10atm). Suitable for swimming and snorkeling.
- Water-tested to 150 meters (500 feet/15atm). Suitable for snorkeling.
- Water Rested to 200 meters (660 feet/20atm). Lowest rating suitable for scuba diving.
- Mil-Spec 300 meters or over (1000 feet/30atm). Suitable for all military applications. 300m is currently the normal standard for divers watches but some exceed this e.g the Rolex Deepsea at 12800ft or 3,900m but quite how that has any practical implication is beyond us but it looks impressive nonetheless.
Please note that we do not recommend swimming or diving with your watch unless it has a screw-down crown (also known as screw-lock or screw-in crown) and is water-resistant to at least 100 meters. Many watches which are rated at 50m/150ft are fine - based on feedback received - but be careful with basic watches that are are only rated to 30m or 99ft. We also recommend caution with watches which use a perspex (plexiglass) crystal because these are quite vulnerable to water ingression and many older or replica watches such as the Timex Vietnam, CWC G10 and W10 as all have have perspex crystals.
Care of a Water Resistant Watch
It is not generally recommended to wear your water resistant watch in a hot shower, sauna or bath although I have always ignored this with all my watches and got away with it so far. The fact remains though that it is not recommended and is at your own risk if you do it because the extreme heat causes the metal parts to expand at a different rate than the rubber gaskets. This creates small openings that can allow small amounts of water to penetrate the watch. Sudden temperature changes are especially harsh if you lie in the sun and then dive into cold water.
After swimming or diving in salt water, immediately rinse the watch in a stream of fresh water. If your watch has a rotating bezel, turn the bezel several times while rinsing it. This will prevent salt buildup and corrosion of the bezel ring.
Some chemicals can corrode the gaskets and make them vulnerable. Heavily chlorinated water can also cause problems, as can chlorine bleach, bath foams, sunscreen and hairsprays that work their way into the watch's seams and damage the gaskets. They can also damage the watch's finish.
Leather straps can be made to be water resistant too. Generally however, leather straps are easily damaged by frequent exposure to water and also start to smell and rot. So if you are going to wear your watch while swimming -- think of buying one with a metal bracelet, or a Nylon NATO strap or other fabric strap although silicon and carbon fibre work well too.