Sound travels approximately four times faster in water than in air.
Why it is true
The density and elasticity of water allow sound waves to propagate at about one thousand five hundred meters per second, compared to three hundred forty meters per second in air.
Source: Acoustics
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.