We discussed this on another forum, and one of the members wrote what I find to be the definitive word on water resistance vs waterproof. So in reference to Joakim Agrin, Here is his original post:
The Water Resistance Myth Vs The Reality!
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The Water Resistance Myth VS The Reality!
Very long Post hope you have the strenght to read it all!
First we need to conclude what is water resistance in the watch world?
In the watch world a watch need to get a IP code rating in order for the mark Water Resistant to appear anywhere on the watch body(notice though that the rating only apply to individual parts not to the whole watch so if a WR rating appears on the wrist
band but not on the case it is not a valid mark for the watch case). So what is IP code rating? well IP stands for International Protection or Ingress Protection. There is different IP codes for different types of "Ingress" protection. In case of Water protection there is 2 certifications. The most common one is the IP code ISO 2281.
ISO 2281:
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. In order to pass for this certification it is not required for each and every individual watch to be subjected to tests, only lot sampling is required.This standard was only designed for watches intended for ordinary daily use during exercises under water for a short period under conditions where water pressure and temperature vary. The tests are:
Immersion of the watch in 10 cm of water for 1 hour.
Immersion of the watch in 10 cm of water with a force of 5 Newton perpendicular to the crown and pusher buttons (if any) for 10 minutes.
Immersion of the watch in 10 cm of water at the following temperatures for 5 minutes each, 40°C(104F), 20°C (68F)and 40°C(104F) again, with the transition between temperatures not to exceed 5 minutes. No evidence of water intrusion or condensation is allowed.
Immersion of the watch in a suitable pressure vessel and subjecting it to the rated pressure for 1 hour. No evidence of water intrusion or condensation is allowed.
Exposing the watch to an overpressure of 2 bar, no more than 50µg/min of air is allowed to get inside the case.
No magnetic or shock resistance properties are required.
No negative pressure test is required.
No
strap attachment test is required.
No corrosion test is required.
So in short it means that the minimum requirement is that the watch will pass a 20 meter(66') test. However if the watch have a different rating then just plain Water resistant for instance a 30M, 50M,100M,200M etc rating then it needs to be tested in a a pressure chamber with a static overpressure equvivalent to the pressure at that depth.
What about Divers watches?
ISO also have a certificate for them to it is called:
ISO 6425
The difference from ISO 2281 is that here not only sampling is required but each and every watch must be tested to 125% to the rated depth so a 200M Divers watch must be tested down to 250M. And also the other tests are much more comprehensive. Here is the list for all the tests and requirements:
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 (104F), 5°C(41F) and 40°C(104F) 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(negative pressure) 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 50µg/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(64.4F) to 25°C(77F) 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.
Additional requirements for mechanical watches are:
Besides water resistance standards to a minimum of 100 meter (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:
The presence of a unidirectional bezel with at least at every 5 minutes elapsed minute markings and a pre-select marker to mark a specific minute marking.
The presence of clearly distinguishable minute markings on the watch face.
Adequate readability/visibility at 25 cm (9.84") in total darkness.
The presence of an indication that the watch is running in total darkness. This is usually indicated by a running second hand with a luminous tip or tail.
Magnetic resistance. This is tested by 3 expositions to a direct current magnetic field of 4,800 A/m. The watch must keep its accuracy to +/- 30 seconds/day as measured before the test despite the magnetic field.
Shock resistance. This is tested by two shocks (one on the 9 o'clock side, and one to the crystal and perpendicular to the face). The shock is usually delivered by a hard plastic hammer mounted as a pendulum, so as to deliver a measured amount of energy, specifically, a 3 kg hammer with an impact velocity of 4.43 m/sec. The change in rate allowed is +/- 60 seconds/day.
Chemical resistance. This is tested by immersion in a 30 g/l NaCl solution for 24 hours to test its rust or corrosion resistance. This test water solution has a salinity comparable to normal seawater.
Strap/
band solidity. This is tested by applying a force of 200 N to each springbar (or attaching point) in opposite directions with no damage to the watch of attachment point.
The presence of an End Of Life (EOL) indicator on battery powered watches.
Watches conforming to ISO 6425 are marked with the word DIVER'S to distinguish diving watches from look a like watches that are not suitable for actual scuba diving.
Most manufacturers recommend diving watches have their seals changed and the watch pressure tested by an authorized service and repair facility every three years or so.
So what do all of this means?
For ISO 2281 watches there is a gigantic range of underwater performance. The ISO 2281 certification does not indicate that a manufacturer must test a watch to failing point and rate it below its failing point, however it must be rated to the maximum pressure test it passed. Its totally up to the manufacturer to descide for each individual watch model exactly what level they want to test it at. So this means that a specific rating is merely a market descision and a way for manufacturers to rate watches differently plainly to justify different price points in their line up of watches. The International Standard Organisation (ISO) have however created a recommendation table that is often found in watch manuals and brochures:
Water resistance rating Suitability:
Water Resistant 30 m or 50 m Suitable for water related work and fishing.NOT suitable for swimming or diving.
Water Resistant 100 m Suitable for recreational surfing, swimming, snorkeling, sailing and water sports. NOT suitable for diving.
Water Resistant 200 m Suitable for professional marine activity and serious surface water sports. NOT suitable for diving.
Diver's 100 m Minimum ISO standard (ISO 6425) for scuba diving at depths NOT requiring helium gas. 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 requiring helium gas. Typical ratings for contemporary diver's watches.
Diver's 300+ m helium safe Suitable for saturation diving (helium enriched environment). Watches designed for helium mixed-gas diving will have additional markings to point this out.
This table of recommendations helps manufacturers to descide what rating to choose and therefor what pressure test level to use depending on the intended use of a watch that they had in mind for a specific model. So this means that if a manufacturers design and development team comes up with a new design to the managment team it is then up to the marketing and managment department of the company to descide first if they will release it to the pucblic and if so to descide what position in their line up it should have. Depending on that descision it will be subjected to different pressure in the over pressure test.