Subnautica Depth Limits and What Watch Water Ratings Mean

A reader wrote to me last summer after her watch fogged up on a snorkelling trip. The caseback said 50 metres, she had never gone deeper than about three, and she was understandably annoyed. Her reasoning was simple: if the number says 50, then three should be nothing. It is the same reasoning anyone who has played Subnautica brings to a dive.

In that game, depth ratings mean exactly what they say. Your little Seamoth submarine is rated to 200 metres, and at 199 it is perfectly safe. Watch water resistance markings do not work that way at all, and the mismatch between the two ideas causes more water-damaged watches than almost anything else I see.

How depth works in Subnautica

Subnautica, released by Unknown Worlds in 2018, is built around going deeper. The Seamoth starts with a crush depth of 200 metres. Depth modules raise that to 300, then 500, then 900. Go past the limit and the hull starts taking damage, with warnings that grow more frantic until the vehicle breaks apart. Stay under it and nothing happens, no matter how long you stay or how hard you drive.

It is a lovely bit of design, because the number is honest and absolute. It also teaches players a rule that sounds sensible and happens to be wrong for watches: the rating is a line, and anything above the line is safe.

What a watch rating actually certifies

For most everyday watches, the depth printed on the dial or caseback refers to a static pressure test under ISO 22810, the standard for water-resistant watches. In a lab, the watch sits still in a chamber while pressure equivalent to that depth is applied, for a short time, at room temperature, with a new gasket and a properly closed crown. That is all the number certifies.

Real life adds things the test leaves out. Water temperature changes make metal and rubber expand and contract at different rates. Soap and sunscreen attack gaskets. A crown pulled out by accident, or a chronograph pusher pressed underwater, opens a direct path inside. Gaskets also age, drying and flattening over years, so a watch that passed at 50 metres when new may not pass at all after five years without service.

So the printed figure is better read as a quality grade than a depth limit. A 30 metre watch is built to cope with rain and handwashing. A 200 metre watch is built with heavier seals and usually a screw-down crown, which leaves much more margin for the messy conditions of a real swim.

A practical reading of common ratings

This is the guide I give people, drawn from manufacturer manuals and what I see coming back across the repair bench. It is conservative on purpose.

Under this reading, my reader's 50 metre watch was rated for gentle pool swimming, not a snorkelling trip in warm salt water with fins and a few dives to touch the sand. It did not fail the test printed on it. It was asked to do a different job.

The myth about moving your arm

You will often hear that swinging your arm underwater creates huge extra pressure, so a swimming stroke could exceed a watch's rating. It makes intuitive sense, and it is mostly wrong. The extra pressure from a fast arm movement is small compared with even a 30 metre rating.

The things that actually let water in are much more ordinary. In roughly the order I see them: a crown that was not screwed down or pushed fully in, a gasket that has not been changed in years, hot water from showers or a spa, and buttons pressed underwater. Notice that none of these appear in a game like Subnautica, where the hull is either intact or damaged and nothing in between. Real seals degrade slowly and silently, which is precisely why people get caught out.

Diver's watches are the exception that proves the point

The one category where the number behaves more like a game rating is the true diver's watch certified to ISO 6425. That standard requires at least 100 metres of resistance and tests each watch beyond its marked depth, at 125 percent of the rated pressure. It also includes checks for things that matter on a real dive, such as legibility in the dark and a bezel that turns in only one direction so an accidental knock can only shorten your timed dive, never lengthen it.

Even then, the certification describes the watch as it left the factory. Divers who rely on their watches have them pressure tested regularly, often once a year, because they know the margin shrinks with every season of salt water and sun. Most watch shops can run a dry pressure test in a few minutes for a modest fee, and it is one of the cheapest forms of insurance in this hobby. I covered the wider routine in caring for a watch so it lasts.

Why this matters for value

Water damage is one of the few faults that can quietly destroy a watch's value. A bit of fogging can mean rust on the hands, a stained dial and corroded parts in the movement, and a dial that has been marked by moisture rarely recovers its original look even after restoration. When I look at a used piece, water marks under the crystal are one of the first things I check, for exactly that reason. It ties into the points in what affects resale value in a used watch.

A Subnautica player can push a Seamoth to 199 metres and come home without a scratch. A watch owner who treats a rating that way will, sooner or later, pay for a dial.

Before your next swim

Check the actual marking on your watch's caseback, then find the date it was last serviced or pressure tested. If the answer is "never" or "more than three years ago", get a pressure test before you take it in the water this season, and screw the crown down every time you get dressed. More game-and-watch crossovers sit in the games section.