Everyone can hear you underwater. They may not understand what you are saying, but they can hear you. Both air and water are made up of millions of tiny little particles. As we make sound, those particles vibrate and pass the vibration along, moving the sound from our mouth to other people’s ears. Over distance, this transfer of sound dissipates until it can no longer be heard. Water particles are a lot more densely packed together than air articles, allowing sound to travel further and faster underwater than in the air.