The water resistance description is theoretical and refers to a water intrusion prevention depth that assumes both the watch and the water are motionless. That never happens in the real world. Such tests are carried out in laboratories under strict conditions. An arm moving under water increases the pressure on the watch as does the movement of the water.

To use a watch for even recreational scuba diving it should have both a screw down crown and a screw on case back. A watch with both of these features will have gasketed protection that will assist in prevent water intrusion. If the watch is a chronograph - it should also have screw down pushers.

1 meter = 3.3 feet
1 ATM (atmosphere) or bar = 10 meters

• Watches labeled "water resistant" can withstand splashes of water but should not be submerged
• "50 Meters" - should withstand very short exposure to water (running your hand under the tap or in a sink for a second)
• "100 Meters" - for use in a swimming pool
• "200 Meters" - for use in recreational scuba diving
• Greater than 200 Meters - suitable for deeper diving
   
• ...and...don't bathe with a watch on. Soap and shampoo suds can reduce the surface tension of the gaskets and allow water to penetrate as well as damage the gasket.