Acoustic waves travel more than four times faster through liquid water than they do through open air

Why sound moves faster through water

Sound is a traveling change in pressure. A vibrating source compresses nearby material, and that pressure disturbance pushes on the material next to it, passing the motion onward. The speed depends on two competing properties: how strongly the material resists compression and how much material must be moved.

Water is much harder to squeeze than air. Its molecules are already packed close together, so a pressure change is handed from one region to the next quickly. Air molecules are far more spread out; the gas is easier to compress, and the pressure disturbance advances more slowly. Water’s greater density works against speed, but its much greater resistance to compression outweighs that effect.

What the speed difference means

In typical conditions, sound travels through water at about 3,300 miles per hour, compared with roughly 767 miles per hour in air. These are approximate speeds, not fixed constants: temperature, pressure, salinity, and the properties of the air can all change them.

The distinction matters underwater. A sound can cover a substantial distance in the time it would take the same sound to travel much less far through air, which helps explain why underwater acoustic signals can carry between distant locations. It is not a simple chain of water molecules flying from the source to the listener: the disturbance travels onward while the molecules mostly vibrate locally, passing pressure changes through the liquid.