From the inception of the first portable timepieces, it has been a preoccupation of watchmakers to protect the delicate mechanisms from the ravages of the elements, particularly dust and moisture. As watches for the wrist gained favor in the 20th century, and watches moved from the protection of the waistcoat pocket to the hazards of exposure on the arm, the need for a watch resistant to water became more critical than ever before.
Today, with modern materials and highly precise manufacturing techniques, it is no longer difficult to produce a watch which will keep moisture from the inside of the watch case. However, how long moisture remains out is a different matter, and this article will explore that, as well as some of the terminology which may confuse the buyer seeking a watch in today's increasingly diverse marketplace.
Watches are properly described as being "water-resistant"--- not"waterproof" as is sometimes heard. The reason for this is quite simple. The term "waterproof" misleadingly implies a state of permanence, and no watch, no matter how water-resistant it may be at the time of manufacture, can be guaranteed to stay that way as the years pass. Watches are typically sealed at critical points, such as the crown, the caseback and the crystal by gaskets which form a seal when under pressure. This effectively keeps water and humidity from the inside of the watch. However, much like the tires of a car which lose their elasticity and grip as they are exposed to seasonal changes, the sealing materials inside a watch gradually lose their ability to maintain a watertight seal. In other cases, hard wearing habits can take a toll, particularly on the winding crown, which if knocked severely, can lose it's allignment with the case tube, diminishing the seal in that critical component.
UV rays, heat, chemicals, and ever airborne pollutants all take their toll, progressively causing the various gaskets to shrink, reducing their ability to be a protective barrier. For this reason, it is important to have one's watch checked, preferably yearly, to ensure that all of the case seals are in good shape. If any gaskets are showing signs of wear, they can be replaced at this time. In this way, the watch can maintain it's water resistance rating, as per it's original factory specifications.
Divers who trust their life to the time a watch provides underwater may prefer to have the gaskets checked frequently, perhaps twice per year. Water resistance is tested in very advanced water-filled pressure chamber which subjects the watches to an overpressure, simulating the exact pressure at a given depth. Typically, the watch cases are tested first, without the movement, and only after this test is passed is the movement placed in the case for final testing.
Several terms are in common usage denoting what the pressure is at a given water depth, and can sometimes cause confusion. The term "atmosphere", sometimes abbreviated "ATM", is another way of expressing a watch's ability to resist water pressure. 1ATM is the equivalent of 10 meters; thusly, a watch watch which is water resistant to 30 meters, could also be said to be protected to 3ATM, while a watch rated for 300 meters, would have 30ATM water resistance. The term "BAR" is sometimes used in lieu of "ATM", and is calculated in exactly the same way, 1 BAR being equal to the pressure encountered at 10 meters of depth. Watches which are intended for serious dive use, and other professional applications are frequently emblazoned with their level of water-resistance, either on the dial, the caseback, or both. The Omega Seamaster Professional, for example, carries on it's dial the notation "300m/1000ft." Similarly, the exceptionally water resistant Seahawk II Pro by Girard-Perregaux, and the Breitling Seawolf Avenger both boldly proclaim their exceptional technical capabilities on their dials.
As a rule, watches rated to less than 50 meters of water resistance, are not recommended for regular immersion, although splashes should not harm such a watch. A watch with a rating of 50 to 60 meters is adequate for swimming, and general water relaxation, such as recreational boating. 100 meters water resistance signifies the beginning of truly "serious" water resistance, and such a watch is capable of use for snorkeling and recreational scuba diving. For professional dive use, 200 meters or more becomes preferable, due to the security margin such ratings provide. Some professional divers, who work in underwater habitats at great depth, are best served by watches with a rating of 1000 meters (3,300 feet) or more. Such watches, which are feats of extreme engineering, provide these professionals with a reassuring safety margin at the extreme depths at which they work.
While the battle has been largely won, and water no longer poses a serious threat to the properly maintained modern watch, it is important that wearers check their watch annually -- regardless of it's depth rating --- to ensure that it's original water resistant cababilities are intact. This is particularly important if the watch is regularly exposed to water immersion. Until an impervious sealing material is invented, these periodic checks will remain a sound precaution for watch owners who want to ensure that their watches continue to give them outstanding service.