Watches are tough little things and some are given water resistance ratings to give that extra utility of having it submerged in water. However, water resistance is not the same as water proof!
Historically, early watches meant for diving use the label waterproof but for it to be technically true, the watch itself has to be sealed with no entry point for leaks at all. This can't be possible since there will always be the hole where your your stem connects the crown with the movement of your watch. That is why wearers are given precautions not to operate the crown when submerged in water. This is especially true if your watch is a mechanical.
When in water, the gasket is the part which keeps the watch protected from outside intrusion. The case back in turn, is protected by ring shaped seals that can be made of Teflon or Viton.
So here are some general tips to keep those important parts from failing you:
- Know your water resistance rating. As a general rule, if a watch has a rating of 3ATM / 30m, treat it as having protection from rain and accidental splashes only. Naturally, the higher resistance rating, the deeper you can use it in water. However, a watch having a water resistance of 20ATM or 200m doesn't really mean it can reach that far without leaking.
- Rinse your watch afterwards. Sea water and swimming pools can take its toll on your watch because of the stuff in contains like salt and chlorine. Even soap can affect the integrity of your seals. Just take it off if it doesn't really need to be under water.
- Have your watch pressure tested once a year. This mostly applies to scenarios where you wear your watch a lot during water-related activities. It's a good idea to check if it's keeping tight.
Don't forget to get your mechanical watch serviced at least every five years. You may not have it near water at all but moisture has a way of getting in to places you don't want them to.