You may be able to wear your watch in the shower. You may even be able to jump in the pool with it on. But there’s a pretty big difference between a waterproof watch and a dive watch.
Before the invention of advanced computerized dive equipment, divers would depend on their watches to keep track of how much time had been spent underwater. The International Organization for Standardization determines what can (and can’t) be called a “dive watch.” The simplest definition comes from Berner’s Illustrated Professional Dictionary of Horology, which says that a diving watch is one “designed to withstand immersion to a depth of at least 100m and to satisfy requirements specified in ISO standard 6425.”