You probably see "30 meters waterproof" in the details of a smartwatch and think that means you can dive up to 30 meters deep with it. Unfortunately, that is not the case!
What does a water resistance of 100 meters mean?
During the water tightness test, a pressure is generated that corresponds to the pressure at a depth of 100 meters. However, this is only static pressure without any movement. The smartwatch/watch must withstand this pressure for a certain amount of time. However, when moving in water, through a shower head or jumping into water, a much higher dynamic pressure is generated. The rules for this pressure test are regulated in the international standard ISO 22810:2010 or the German DIN 8310. However, since this test does not define real swimming or diving depths, the following classification has become established:
|30 meters||3 Bar||washing hands / splash water|
|50 meters||5 Bar||bath / shower|
|100 meters||10 Bar||swimming / snorkeling|
|200+ meters||20+ Bar||diving|
What's the connection between 10 ATM and 100 meters water resistant?
"ATM" stands for "physical atmosphere" and is a formerly common unit for pressure. In the watch industry, it has persisted to this day. Since it cannot be exact by definition (see Wikipedia for more), it was replaced by the unit "bar" in Germany and Austria in 1978. 1 bar corresponds approximately to the air pressure on the surface of the earth or a water column of 10 meters height. 10 ATM corresponds to about 10 bar, which is approximately the pressure that prevails at a depth of 100 meters. This is where the term "100 meters water resistant" comes from.
Why is there no simple classification?
As described above, the ISO 22810:2010 standard only regulates the static pressure that a watch must withstand. However, in real life, this specification is pretty worthless. For example, if you jump from the edge of the pool flat into the water, the watch must withstand much higher pressure than if you let it slide gently to the bottom in the pool. In the first case, the watch may be exposed to water depths of only 30 cm, in the second case 1.50 meters. Nevertheless, the risk of water collapse is much greater in the first example because of the higher dynamic pressure.