Original: Substances with a specific gravity of 1 are neutrally buoyant , those with SG greater than one are denser than water , and so ( ignoring surface tension effects ) will sink in it , and those with an SG of less than one are less dense than water , and so will float .
Simplified: Substances with a specific gravity greater than 1 are heavier than water , and those with a specific gravity of less than 1 are lighter than water .