What are the various levels of water-resistance?

Watches with the lowest level of water resistance are labeled simply "water-resistant." They can withstand splashes of water but should not be submerged.

1 Atmosphere / 33 Feet / 10 Meters: A watch with this resistance level is protected against accidental exposure to water; for example, splashes, perspiration or accidental immersion. It should not be exposed to any water pressure.

3 Atmospheres / 100 Feet / 30 Meters: Not sufficiently resistant for swimming but will withstand splashes or brief immersion in water.

5 Atmospheres / 165 Feet / 50 Meters: Suitable for playing sports and swimming in shallow water.

10 Atmospheres / 330 Feet / 100 Meters: Suitable for playing sports, active swimming or poolside diving.

15 Atmospheres / 500 Feet / 150 Meters: For playing sports, active swimming or poolside diving and also suitable for snorkeling.

20 Atmospheres / 660 Feet / 200 Meters: For playing sports, active swimming or poolside diving. It will also allow skin diving and scuba diving at depths not requiring helium gas.

**You must not press the buttons on a watch while the watch is submerged in water, or still wet , nor pull out the winder while the watch is submerged in water.

Is water resistance permanent?
No. Water resistance depends on several factors some of which can be affected by wear or simply by time. Gaskets can become corroded or misshapen, cases dented or crystals loose or broken. That's why your watch, like your car and your teeth, needs preventive maintenance. Most manufacturers say water resistance needs to be tested every time the case back is opened, because opening the case can dislodge the gaskets. This rule applies even to a simple battery change.

Exposing your watch to heat, whether it's in a hot tub or sauna can cause the gaskets to lose their shape and their ability to keep out water. Also some chemicals can corrode the gaskets and make it vulnerable. Heavily chlorinated water can cause problems, as can spray-on perfumes and hairsprays that work their way into the watch's seams and damage the gaskets. (They can also damage your watch's finish.)