A few weeks after opening this online store, I decided I wanted to know exactly what the water resistant numbers meant. I would read that a watch is 30M water resistant but is only splas proof - how does that work?
People are often confused by what the stated water resistance of watches actually means. Does a watch with '30 metres or 30M' as the water resistance mean you can dive with it as deep as 30 metres' No, you can not. So why do they write 30 metres on it?This is referring to static pressure, not the actual depth of water it can be used in. This is a common misconception.
30 metres refers to the pressure experienced if it was static at a depth of 30 metres. When the watch moves the pressure rises well above a static pressure of 30 metres. 30 metres of static water pressure is easily achieved even in shallow depths. Consequently, a 30 metres watch should not be used for diving, however it can be immersed in water.
Here are some common explanations of common water resistance standards:
Water resistant means splash proof only - it can withstand slight splashes and rain, but is NOT to be immersed in water.
The list below outlines the general guidelines of the water resistancy you will receive from an accordingly rated watch.
Splash proof and waterproof in small amounts of water
Can be submerged in water. Suitable for swimming, but not guaranteed to be resistant to jumping into the pool.
Suitable for swimming and shallow diving
Suitable for diving - not deep sea.
If you have the battery in your watch changed, you should be sure to have it resealed and pressure tested by the jeweller to ensure that it is still water resistant to the stated depth.