Deep Is Fine, Heat and Grease Are Not
Sunscreen can damage the watch gaskets, while steam and extreme temperature fluctuations, like in a sauna or steam room, may cause them to contract or expand. When this happens, water can enter the timepiece—precisely the scenario it was designed to avoid.
Give it a Freshwater Bath
While a real dive watch is designed to resist corrosion, you should always rinse it in fresh water after a dip in the sea. Turn the bezel as you do to fully flush out salt water and sunscreen, which can degrade the seals. Don’t use soap or other chemicals — the H2O alone will suffice — and dry the watch after rinsing.
Service and Protect
Plan to have your watch professionally pressure-tested every three to five years and, if necessary, have the gaskets replaced. Those tiny rubber O-rings are the only things preventing an expensive repair. Even if you’ve inherited a vintage diver and the only bar pressure it will see is trivia night at the local pub, get it serviced anyway: the natural oils lubricating the movement may be dry.