The property that compares the density of a substance with that of water is called specific gravity.

Here's a breakdown:

* Density: A measure of how much mass is contained in a given volume.

* Specific Gravity: A dimensionless ratio of the density of a substance to the density of a reference substance (usually water at 4°C).

So, a specific gravity of 1 means the substance has the same density as water. A specific gravity greater than 1 means the substance is denser than water, and a specific gravity less than 1 means it is less dense than water.