A 200 m rating means the watch can be worn swimming, snorkelling and recreational diving. It does not mean you can take it two hundred metres underwater. The number is a pressure rating measured in a laboratory on a new, static watch, not a promise about depth.
Why the number is not a depth
Water resistance is tested by applying static pressure equivalent to a column of water of that height. Real swimming is not static. Diving into a pool, swinging your arm through a stroke, or holding your wrist under a tap all create brief pressures far higher than depth alone would suggest.
That is why the practical guidance for each rating is much more conservative than the number printed on the dial.
What each rating actually permits
30 m / 3 ATM. Splashes, rain, washing your hands. Not swimming. This is the standard rating for dress watches, including much of Slim Line and Ora Vera.
50 m / 5 ATM. Brief swimming and showering. Not diving off anything, and not repeated daily immersion.
100 m / 10 ATM. Comfortable swimming and snorkelling. Fine for a holiday, fine for a lake.
200 m / 20 ATM. A genuine dive rating. Swimming, snorkelling and recreational scuba. This is where the Aquarider sits, with a unidirectional bezel and a screw-down crown.
Why the bezel only turns one way
A diver's bezel rotates counter-clockwise only. You align the marker with the minute hand when you enter the water and read your elapsed time off the bezel.
If the bezel could turn both ways, a knock could rotate it the wrong direction and make a dive look shorter than it was. Turning only counter-clockwise means any accidental movement makes the dive look longer, which is the safe direction to be wrong in.
The two rules that matter more than the rating
Never operate the crown or pushers in water. Almost every case of water ingress on a modern watch begins with an unscrewed or partially pulled-out crown. Screw the crown down fully before you go near water.
Have the gaskets tested. Water resistance depends on rubber, and rubber hardens with age and heat. A watch rated at 100 m when it left Switzerland may not hold 100 m eight years later if nobody has checked it. If you swim with your watch, have the water resistance pressure-tested annually. It is quick and inexpensive.
What to avoid regardless of the rating
Hot showers, saunas and hot tubs. Heat expands metal and rubber at different rates and is the fastest way to compromise a seal. Salt water is fine on a rated diver, but rinse the watch in fresh water afterwards, because dried salt is abrasive and works into the bezel and bracelet.
What to do if you see condensation
Act immediately. Moisture inside a case corrodes the movement, and corrosion is not reversible. Take the watch to a watchmaker the same week, even if it clears on its own. Read more on that in our piece on servicing.
Common questions
Can I shower with a 50 m watch?
Occasionally, yes, if the crown is fully closed. Regularly, no. The heat and the soap are harder on the gaskets than the water.
Is 100 m enough for swimming?
Yes, comfortably, including snorkelling. For repeated diving choose 200 m.
What is the difference between ATM and metres?
They are the same measurement expressed differently. 1 ATM is roughly 10 metres of static pressure, so 20 ATM and 200 m mean the same thing.
Does water resistance wear out?
The gaskets do. The rating is a property of the seals, not of the case, and seals age whether or not you swim.