Very interesting. It makes sence that sound would travel faster in water than air because it is more dense. Indeed, sound travels faster yet through solid materials.
Light on the other hand travels more slowly through denser gases than air, and water. The speed of light through a vacuum is 3x10^8 m/s. Its speed through any medium, such as a liquid or gas is multiplied by its index of refraction, which is generally a decimal; yielding a smaller value, i.e. a lower speed.
This was a very informative post! Thank you!