Can I wear my watch in the ocean?

Yes, with three conditions: a rating of 100 m or more, a crown screwed fully home before you go in, and a fresh water rinse when you come out. A watch rated 200 m or carrying the DIVER'S marking of ISO 6425 is the comfortable choice, because that standard actually includes a salt water test.

Ocean water is the harshest routine environment a watch encounters, and almost none of the harm happens while you are swimming. It happens afterward, when the water evaporates and leaves salt behind in every crevice on the case.

What rating you actually need

What salt, chlorine and sand each do

Salt attacks metal electrochemically, and it does its worst work in tight gaps where oxygen cannot reach and rinsing does not either. That is textbook crevice corrosion: the gap between an end link and a lug, the underside of a clasp, the seat a bezel rotates in. Stainless steel resists it well in open air and much less well in a chloride-rich crevice that stays damp for weeks.

Chlorine from a pool is a different attack. It is harder on the elastomer gaskets than on the case, and combined with warm pool water it shortens seal life noticeably. It also dulls some case finishes and can pit steel over long exposure.

Sand is purely mechanical and often the most immediate problem. A grain caught in a bezel raceway grinds the click spring teeth and the bezel gasket every time you turn it. A grain in the crown threads can hold the crown a fraction of a millimeter off its seat, which is enough to break the seal entirely. Sand under a caseback edge or in a spring bar hole does damage you never see until a service.

Before you go in: the 20 second check

• Crown. Screwed fully home, or pushed completely in. Half a turn loose and the rating is gone. This is the single most common cause of a flooded watch at the beach.
• Pushers and any helium valve. Screw-down pushers on a chronograph must be locked down. Do not press them in water at all.
• Crystal and case. Look for chips, a cracked crystal, or a caseback that feels loose. Any of those means stay out.
• Strap or bracelet. Check spring bars and clasp. Salt water is where watches get lost, not just flooded.
• Recent case opening. If a battery was changed or a caseback was off and the watch has not been pressure tested since, treat the rating as unknown.

The rinse routine that prevents most damage

1. Check the crown is still screwed down before the rinse, not after. Rinsing with an open crown is worse than not rinsing.
2. Rinse in cool fresh water. A running tap works; a few minutes soaking in a bowl of fresh water works better, because dissolving salt takes time.
3. Turn the bezel back and forth under the water so the rinse reaches beneath it, and flex the bracelet so water moves between the links and through the clasp.
4. Never use hot water. Heat is harder on gaskets than the ocean is, so a hot rinse trades one problem for a worse one.
5. Dry it properly. Soft cloth, then somewhere airy. Water trapped under a bracelet corrodes spring bars and end links quietly for weeks.

After the season: what to have checked

A watch that swims in the sea deserves a pressure test roughly once a year, and a dry test on a bench typically runs roughly $25 to $60 in the US before sales tax, though what a shop charges varies from one city to the next and again from one country to the next. Ask for fresh gaskets whenever the case is opened for any reason.

Beyond that, look at the bracelet. Salt hides in clasps and end links, and a watchmaker removing the bracelet during a service will find it. If the watch has spent a season in the ocean and the bezel feels gritty or the crown no longer screws down smoothly, get it looked at before the next trip rather than after it. The servicing and care guide covers what gets replaced, and the case materials guide explains why plated and coated cases behave differently from solid steel in salt water.