Water Resistance Ratings Explained

What each rating actually permits

Why the numbers overstate what you can do

Three reasons, and they compound:

• The test is static. Pressure is applied to a stationary watch. Swinging your arm through water, diving in, or the jet from a shower head all create momentary pressures far above the static equivalent of your actual depth.
• The test is on a new watch. Gaskets are rubber; they compress, dry out and age. A five-year-old 100m watch that has never been pressure-tested is not a 100m watch any more.
• Heat opens things up.A hot shower or a sauna expands the case and the seals at different rates, and steam is small enough to pass where liquid water wouldn't. That's why even 100m watches shouldn't live in the shower.

The hardware that actually matters

A screw-down crown is the single most important feature. The crown is the biggest hole in the case; a push-pull crown relies on a gasket alone, while a screw-down crown threads shut and compresses the seal. Almost every genuine 200m watch has one — the Orient Mako II, Seiko Turtle and Casio Duro all do.

A screw-down or solid caseback matters next. Display backs are common at 50m and 100m and rare above that; the exhibition-caseback shortlist notes which picks keep a decent rating anyway. And crystal thicknessis the third factor — a dive watch's crystal is thicker and better seated than a dress watch's.

ISO 6425 and what "diver's watch" means

There is a formal standard, ISO 6425, that governs which watches may be marketed as diver's watches. It requires more than a pressure figure: legibility in darkness, a unidirectional bezel with elapsed-time markings, resistance to shock, magnetism and salt water, and testing of a percentage of production rather than a sample design.

A watch can be genuinely 200m water resistant without being ISO certified — the Casio Duro is the obvious example. For swimming and snorkeling that difference is academic. For actual scuba diving, buy certified: the Citizen Promaster Fugu is the ISO-rated pick on our dive list.

Practical rules we'd actually follow

• Never operate the crown or a chronograph pusher underwater, at any rating.
• Always check the crown is screwed down before water. This is the most common failure.
• Rinse in fresh water after the sea. Salt destroys gaskets and eats bezel bearings.
• Keep every watch out of hot showers, saunas and hot tubs regardless of rating.
• If condensation ever appears under the crystal, stop wearing it and have the seals checked — that's water inside the case, and it will rust the movement.
• Have gaskets replaced when the watch is serviced, or pressure-tested every few years if you swim in it regularly.

What rating should you buy?

For one watch that does everything, 100m minimum and 200m with a screw-down crown if you want to stop thinking about it entirely. A 30m or 50m rating is fine on a dress watch you wear to occasions — the dress-watch picks mostly sit there — but it is the wrong choice for a watch you wear daily. Our dive roundupis the shortest route to a 200m watch that isn't expensive.