Why There Are Not Any Waterproof Watches
One watch concepts that is hard to understand is the notion of a watch being “water resistant” to a particular depth. Rolex’s Deep Sea is “water resistant” to a depth greater than what a human can survive, yet the watch is not considered “water proof.” The term “waterproof” was discontinued in the late 1960’s because several government organizations including the Federal Trade Commission investigated truth of product labeling and advertising.
The FTC realized “waterproof” misrepresented products, specifically diving-type watches never have been completely under normal use at specific depth ratings. Subsequently, “water resistant” is used to describe watches water impenetrability to a stated depth. There are no technical differences between a waterproof watch and a water resistant watch. The same engineering design and techniques are used to keep the inside of a watch case dry.
Water resistance of a watch is based in pressure tests comparable to a swimmer or still sitting diver at a particular pressure level. The degree of water resistance differs according to whether the watch is moving and pressure changing dynamically through water or whether standing still at a static level/pressure.
Here’s the real scoop: Water resistance of watches is rated based on a laboratory pressure tests comparable to a swimmer or diver sitting still at that pressure level. But many water-based activities involve a lot of movement and other environmental changes. These exceptions to how the watch was rated may challenge or defeat the water protection features of a water resistant watch. A watch for a jet or water skier will need to be higher rated because of the increased pressure when the watch hits the water for speed. The same is true for watches used in the bathtub with little dynamic pressure; a watch in this setting can use a lower water resistance rating.
Below is a chart of water resistance posted by Casio.
All modern Rolex watches are rated at 100 Meters which is a conservative measure, and Rolex dive watches are rated at a minimum of 300 meters. Regardless of the depth rating, Rolex uses conservative design and many believe that the advertised depth rating is 25% lower than actual. Just be sure to keep the winding crown screwed in, and to have the watch pressure tested by your local watch maker every year to insure water tightness.