The guy you are responding to is joking, but the whole planet is kind of made of water with land floating on it. It's not just water though; it's rock that is saturated with water. There is a lot of water in the crust, then the upper mantle is pretty dry, but 400 km deep there is a lot of water, possibly more than in all the oceans combined. It's the boundary between the outer mantle and the inner mantle. That transition zone is about 7% of the Earth's mass and probably between 1 and 3% of it is water. That puts it at 1.5 to 4.5 times as much water as there is in the crust.