Water resistance

Relating to watches, "water resistance" – not "waterproof" – is the correct term to use. Here are some guidelines on the main categories: non-water resistant cases, water resistant cases and diver cases.
 

Non-Water Resistant Cases
These are mostly dress watches made with thin gaskets that provide only minimal moisture protection. Some do include plastic or metal shields around the stem to prevent dust from entering, but water will still penetrate.
 

Identification:If there's no mention of water resistance anywhere on the back of the case, it's not water resistant.
 

Use limits:These cases will resist everyday dust, humid summer days or an accidental splatter in the kitchen sink. But avoid prolonged exposure to steam from boiling water while cooking or any extended full water exposure. No swimming or bathing while wearing the watch.
 

Water-Resistant Cases
Identification: The case or dial will say "water resistant" for the minimum classification. When this is accompanied by a number, it indicates the depth below sea level and accompanying pressure the watch can withstand when new. Look for an ATM (atmospheres) marking or the term "water resistant" combined with a figure of, say, 50 meters (5 ATM). The rating is determined by a testing device when all the gaskets are fresh.
 

Use Limits (see table at bottom):Because one doesn't normally replace or test the watch gasket annually,  one should buy a watch rated to withstand the most extreme condition you will likely encounter.
 

Frequent swimmers may consider at least a 100-meter watch; casual swimmers may do fine with a 50-meter watch.
 

Frequent use during sports would likely require at least a 100-meter rating to keep out perspiration.
 

Professional Diver Case
Identification:These cases are rated at 300 meters or greater and have heavy gaskets and crystals intended for use at scuba depths.
 

Use Limits : Few. If you are a serious diver, we suggest that you bring the watch in for an annual pressure test and/or gasket replacement to be sure the heavy gaskets are tight and don't leak.
 

General Precautions
With any water-resistant watch, you are reminded not to operate the crown or push buttons while underwater. It is also important to dry the case before setting the watch.
 

If the crown is a screw-down or locking type, be sure it's in place before diving or swimming. Also note that chemical solvents can penetrate many water-resistant cases. If these are nearby, they may affect the water resistance of the watch.