Which substance is heavier: water or fuel?

Water is denser than most types of fuel, which makes it a heavier substance when compared by volume. The density of water is about 8.34 pounds per gallon, while various types of aviation fuels, such as Jet A, have densities that typically range from 6.5 to 7.5 pounds per gallon. This difference in density means that when comparing equal volumes, water will weigh more than fuel. Therefore, water is indeed heavier than fuel, making it the correct answer to the question.

Considering that fuel density can vary based on its composition, it might be easy to assume that some fuels could be heavier. However, in general practice, water remains the heavier substance, reinforcing the comparison effectively.