This Demonstration calculates the speed of sound for a homogeneous mixture of water and air. Surface tension is neglected for air bubbles in water or water droplets in air, and density is assumed independent of temperature for simplicity. It is shown that the speed of sound is much lower for a large range of mixing ratios than the speed of sound in either air or water alone. The speed of sound in the mixture is determined predominantly by the density of water and the compressibility of air.