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A watch rated as Water Resistant may come in contact with water to a predetermined extent. Most watches are classified by the degree until which depth of immersion is safe. It is important to remember that a water resistant rating is based on optimum conditions in a laboratory. Real life experience and aging of the gaskets will effectively decrease the manufacturer's specifications of water resistance over time. The worst case scenario that can happen to a watch is when water comes into contact with the movement. We strongly suggest to work well within the parameters of the manufacturer's recommendations and have your watch tested at least once a year. Any experienced watchmaker has the necessary equipment to test water resistance.

Water Resistance Factors

There are three essential factors to obtain the water resistance on a watch:

  1. Crown: The single most important factor in ensuring water resistance. The weakest part of a watch for water to penetrate is the crown-stem hole. The stem of the crown is attached to the movement through a hole in the case edge. The crown is constantly moved to different positions, wound and turned to correct the time, and the gasket is continuously compressed, chafed and stressed. The slightest variation in the shape of the gasket or if the crown is not pushed all the way in will allow water to penetrate the watch through the stem hole.
    • Screw-Down Crowns are threaded and screw shut to a matching threaded tube in the case. The crown has a gasket that is compressed and seals the opening when the crown is tightened - thus ensuring water resistance. A screw-down crown is an essential feature for any watch intended for swimming, and we do not recommend swimming with a watch that does not have a screw-down crown. However, even if the watch has a screw-down crown and chronograph pushers, the crown and pushers should never to be pushed, adjusted or opened when the watch is immersed in water (unless otherwise stated by the manufacturer). An additional benefit of the screw-down crown is that the crown has more protection from accidental knocks.
  2. Caseback: This refers to how the case back is attached to the watch. Snap-on casebacks are sealed by pressure and are considered the least water resistant. The slightest nick in a case or deformity in a gasket (which happens over time) will allow water to penetrate the case. Generally, these watches will have a water resistance of 30m/99ft maximum - which allows for contact with water but not immersion.
    • Casebacks attached with screws would be the next level of water resistance. Having the caseback attached with screws allows for a much tighter seal than a snap-on caseback. However, a deformity in the gasket will still allow water to penetrate. Generally, these watches will have a water resistance of 100m/330ft maximum - which allows for light swimming and immersion in a pool.
    • Screw-in casebacks are threaded and screwed into the actual case. The screw-in casebacks create a double seal, using both the threading and the gasket as a seal. Generally, diving watches with water-resistant ratings greater than 100m/330ft will have this type of caseback.
  3. Gaskets: Also known as "O" rings are made of rubber, nylon or Teflon which form watertight seals at the joints (where the crystal, caseback, and crown meet the watch case). If the watch is a chronograph, the chronograph pushers will also have gaskets.
    • Gaskets begin to erode and break down over time, diminishing the water resistance of a watch. It is important to test your watch once a year for water resistance. Any experienced watchmaker should have the necessary equipment to test the watch - the cost should be minimal.

Real Life Applications and Water Resistance

When the manufacturer tests a watch, it is done in a laboratory under optimum conditions, such as a fresh gasket, sitting stationary in a pressured water tank and with still/motionless water. However, real-life scenarios will produce completely different results. Here are a few scenarios:

Water Resistance vs. Water-Proof

The U.S. FTC (Federal Trade Commission) which enforces the truth-of-advertising has deemed the term "Waterproof" inappropriate. In their opinion, a watch can never be 100% truly impervious to water, as the gaskets deteriorate over time and exposure, thus reducing the specified depth of water resistance. In the words of the FTC "The word proof connotes a measure of absolute protection that unfortunately does not exist with respect to watches, especially over prolonged periods of time." The FTC has found the term Water Resistant to be more appropriate.

Water Resistance Testing Methods

There are two commonly used water resistance testing methods:

  1. Dry Test: The watch is placed in a chamber, and the air pressure is increased. The machine detects the smallest variation in the case size. If the case expands, even slightly, then the watch is not water resistant.
  2. Wet Test: The watch is placed in a chamber that is filled with half water and half air. Air pressure is increased while the watch is out of the water. The watch is then slowly immersed in the water. Once the watch is completely submerged, the air pressure is slowly released. If bubbles come out of the watch, it means that air seeped into the watch before being immersed in the water and the watch is not water resistant. This method is generally used as a second test to pinpoint the problem area.


ATM is short for "Atmosphere" which is equal to 10 meters. Another word for ATM which is commonly used in Europe is BAR - this too is equal to 10 meters.

Helium Escape Valve

Helium Escapement Valve

The Helium Escape/Relief Valve is used only in extreme deep diving expeditions when a diver operates from a diving bell. As the bell is lowered, pressure begins to increase, and helium is added to the breathing mix. The helium is added to remove toxic air created by the extreme depth.

Helium is one of the smallest molecules and will seep into the watch through the seals until the air pressure in the watch equals the air pressure in the diving bell. As the diving bell surfaces and decompresses, the helium needs to escape from the watch at the same speed as the decompression (otherwise the pressure in the watch will pop the crystal off. To avoid that, Omega developed the helium escape valve which allows the helium to escape faster than it seeps in. Many brands use the escape valve in one design or another. Generally, the escape valve can be found on watches which have a water resistance rating of 300m or greater.

The helium escape valve is never needed when scuba diving (unless your diving in a controlled environment as described above).

Interpretation of the Depth Ratings

Although a watch may have a rating of 30m/99ft water resistant, it does NOT mean that the watch can be immersed in that depth of water. The depth rating posted by the manufacturer is theoretical and can only be achieved in the perfectly optimum environment of a laboratory (which is impossible to replicate in real life).

No Rating - 30m/99ftDoes not allow contact with water
30m/99ft - 50m/165ftContact with water such as washing hands and rain
50m/165ft - 100m/330ftLight poolside swimming
100m/330ft - 200m/660ftSwimming, snorkeling, showering (no hot water)
200m/660ft - 500m/1650ftImpact water sports such as board diving and scuba diving
500m/1650ft+Appropriate for serious deep water diving.

Moreover, the higher the rating, the more appropriate the watch is for deeper diving.

IMPORTANT: We strongly recommend purchasing a watch with a screw-down crown if you intend on wearing the watch while you are in contact with water.