Sound travels faster under water than in the air. Sound waves travel by conduction from one molecule to another. Water molecules are much closer together than air molecules, facilitating the speed of the sound wave.
A sound wave travels at a speed of approximately 5,000 feet per second under water. This is about four times faster than sound waves travel in the air. Colder water temperatures cause a decrease in the speed of the sound wave, and so a sound wave at a greater depth travels slower than a sound wave close to the surface. The increased speed of transmission also allows sounds to travel a greater distance under water than in the air.