Diving Watch - Water Resistance

Water Resistance

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.

Water resistance is achieved by the gaskets which forms a watertight seal, used in conjunction with a sealant applied on the case to help keep water out. The material of the case must also be tested in order to pass as water resistant.

None of the tests defined by ISO 2281 for the Water Resistant mark 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 scuba diving.

The standards for diving watches are regulated by the ISO 6425 international standard. The watches are tested in static or still water under 125% of the rated (water) pressure, thus a watch with a 200 meter rating will be water resistant if it is stationary and under 250 meters of static water. The testing of the water resistance is fundamentally different from non-dive watches, because every watch has to be fully tested.

ISO 6425 water resistance testing of a diver's watch consists of:

• Immersion of the watch in 30 cm of water for 50 hours.
• Immersion of the watch in water under 125% of the rated pressure with a force of 5 N perpendicular to the crown and pusher buttons (if any) for 10 minutes.
• Immersion of the watch in 30 cm of water at the following temperatures for 5 minutes each, 40 °C, 5 °C and 40 °C again, with the transition between temperatures not to exceed 1 minute. No evidence of water intrusion or condensation is allowed.
• Immersion of the watch in a suitable pressure vessel and subjecting it to 125% of the rated pressure for 2 hours. The pressure must be applied within 1 minute. Subsequently the overpressure shall be reduced to 0.3 bar within 1 minute and maintained at this pressure for 1 hour. No evidence of water intrusion or condensation is allowed.

• For mixed-gas diving the watch has to be immersed in a suitable pressure vessel and subjecting it to 125% of the rated pressure for 15 days in a (helium enriched) breathing gas mix. Subsequently the overpressure shall be reduced to normal pressure within 3 minutes. No evidence of water intrusion, condensation or problems caused by internal overpressure are allowed.
• An optional test originating from the ISO 2281 tests (but not required for obtaining ISO 6425 approval) is exposing the watch to an overpressure of 2 bar, no more than 50 µg/min of air is allowed to get inside the case.

Except the thermal shock resistance test all further ISO 6425 testing should be conducted at 18 °C to 25 °C temperature. 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 can not nearly swim that fast) physics dictates that the diver generates a dynamic pressure of 0.5 bar or the equivalent of 5 meters of additional water depth.