Water Resistant is a common mark stamped on the back of wrist watches to indicate how well a watch is sealed against the ingress of water. It is usually accompanied by an indication of the static test pressure that a sample of newly manufactured watches were exposed to in a leakage test. The test pressure can be indicated either directly in units of pressure such as bar, atmospheres, or (more commonly) as an equivalent water depth in metres (in the United States sometimes also in feet).
An indication of the test pressure in terms of water depth does not mean a water-resistant watch was designed for repeated long-term use in such water depths. For example, a watch marked 30 metres water resistant cannot be expected to withstand activity for longer time periods in a swimming pool, let alone continue to function at 30 metres under water. This is because the test is conducted only once using static pressure on a sample of newly manufactured watches. As only a small sample is tested there is likelihood that any individual watch is not water resistant to the certified depth or even at all. The test for qualifying a diving watch for repeated usage in a given depth includes safety margins to take factors into account like aging of the seals, the properties of water and seawater, rapidly changing water pressure and temperature, as well as dynamic mechanical stresses encountered by a watch. Also every diving watch has to be tested for water resistance or water-tightness and resistance at a water overpressure as it is officially defined.
The International Organization for Standardization issued a standard for water-resistant watches which also prohibits the term waterproof to be used with watches, which many countries have adopted. This standard was introduced in 1990 as the ISO 2281:1990 and only designed for watches intended for ordinary daily use and are resistant to water during exercises such as swimming for a short period. They may be used under conditions where water pressure and temperature vary; German Industrial Norm DIN 8310 is an equivalent standard. However, whether they bear an additional indication of overpressure or not, they are not intended for submarine diving.
The ISO 2281 standard specifies a detailed testing procedure for each mark that defines not only pressures but also test duration, water temperature, and other parameters. Besides this ISO 2859-2 Sampling plans indexed by limiting quality (LQ) for isolated lot inspection and ISO 2859-3 Sampling procedures for inspection by attributes – Part 3: Skip-lot sampling procedures concerning procedures regarding lot sampling testing come into play, since not every single watch has to be tested for ISO 2281 approval.
ISO 2281 water resistance testing of a watch consists of:
Except the thermal shock resistance test all further ISO 2281 testing should be conducted at 18 °C to 25 °C temperature. Regarding pressure ISO 2281 defines: 1 bar = 105 Pa = 105 N/m2.
This has since be replaced by the ISO 22810:2010 standard, which covers all activities up to specified depth and clears up ambiguities with the previous standard.
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.
The standards and features for diving watches are regulated by the ISO 6425 – Divers' watches international standard. This standard was introduced in 1996. ISO 6425 defines such watches as: A watch designed to withstand diving in water at depths of at least 100 m and possessing a system to control the time. Diving watches are tested in static or still water under 125% of the rated (water) pressure, thus a watch with a 200-metre rating will be water resistant if it is stationary and under 250 metres of static water. ISO 6425 testing of the water resistance or water-tightness and resistance at a water overpressure as it is officially defined is fundamentally different from non-dive watches, because every single watch has to be tested. Testing diving watches for ISO 6425 compliance is voluntary and involves costs, so not every manufacturer present their watches for certification according to this standard.
ISO 6425 testing of a diver's watch consists of:
Except the thermal shock resistance test all further ISO 6425 testing should be conducted at 18 to 25 °C temperature. Regarding pressure ISO 6425 defines: 1 bar = 105 Pa = 105 N/m2. The required 125% test pressure provides a safety margin against dynamic pressure increase events, water density variations (seawater is 2% to 5% denser than freshwater) and degradation of the seals.
Movement induced dynamic pressure increase is sometimes the subject of urban myths and marketing arguments for diver's watches with high water resistance ratings. When a diver makes a fast swimming movement of 10 m/s (32.8 ft/s) (the best competitive swimmers and finswimmers do not move their hands nor swim that fast) physics dictates that the diver generates a dynamic pressure of 50 kPa or the equivalent of 5 metres of additional water depth.
Besides water resistance standards to a minimum of 100 metres (330 ft) depth rating ISO 6425 also provides minimum requirements for mechanical diver's watches (quartz and digital watches have slightly differing readability requirements) such as:
Diving at a great depth and for a long period is done in a diving chamber, with the (saturation) diver spending time alternately in the water and in a pressurized environment, breathing a gas mixture. In this case, the watch is subjected to the pressure of the gas mixture and its functioning can be disturbed. Consequently, it is recommended to subject the watch to a special extra test. ISO 6425 defines a diver's watch for mixed-gas diving as: A watch required to be resistant during diving in water to a depth of at least 100 m and to be unaffected by the overpressure of the mixed gas used for breathing.
The following specific additional requirements for testing of diver's watches for mixed-gas diving are provided by ISO 6425:
Most manufacturers recommend divers to have their diving watch pressure tested by an authorized service and repair facility annually or every two to three years and have the seals replaced.
Watches are often classified by watch manufacturers by their degree of water resistance which, due to the absence of official classification standards, roughly translates to the following (1 metre ≈ 3.29 feet). These vagueries have since been superseded by ISO 22810:2010, in which "any watch on the market sold as water-resistant must satisfy ISO 22810 – regardless of the brand."
|Water resistance rating||Suitability||Remarks|
|Water Resistant 3 atm or 30 m||Suitable for everyday use. Splash/rain resistant.||Not suitable for showering, bathing, swimming, snorkeling, water related work, fishing, and diving.|
|Water Resistant 5 atm or 50 m||Suitable for everyday use, showering, bathing, shallow-water swimming, snorkeling, water related work, fishing. Splash/rain resistant. [better source needed]||Not suitable for diving.|
|Water Resistant 10 atm or 100 m||Suitable for recreational surfing, swimming, snorkeling, sailing and water sports.||Not suitable for diving.|
|Water Resistant 20 atm or 200 m||Suitable for professional marine activity, serious surface water sports and skin diving.||Suitable for skin diving.|
|Diver's 100 m||Minimum ISO standard (ISO 6425) for scuba diving at depths not suitable for saturation diving.||Diver's 100 m and 150 m watches are generally old(er) watches.|
|Diver's 200 m or 300 m||Suitable for scuba diving at depths not suitable for saturation diving.||Typical ratings for contemporary diver's watches.|
|Diver's 300+ m for mixed-gas diving||Suitable for saturation diving (helium enriched environment).||Watches designed for mixed-gas diving will have the DIVER'S WATCH xxx M FOR MIXED-GAS DIVING additional marking to point this out.|
ISO 22810:2010, Horology – Water-resistant watches, has been drawn up to meet a global demand for clear and unambiguous specifications in this area. It clarifies the terms used, defines the criteria to be met by the product and specifies the marking which may appear on the product.