Sound travels through water at a speed of around 3316 miles per hour or 1.482 kilometers per second. That is about 4.3 times faster than sound travels through air. The speed changes slightly depending on the salinity of the water.
Despite the speed of sound being higher in water it is easier for humans to hear sounds through air. This is partly because the eardrums cannot vibrate when the outer portion of the ear is filled up with water. The type of vibrations human ears use to hear sound under water are also less effective than those they use in air. Sound waves travel even faster through solids than through liquids or gases.