The density of salt water is 1.025, making it heavier than freshwater. Because of this, if the two types of water are mixed, the salt water sinks to the bottom while the freshwater floats on top.
One easy way to demonstrate the difference in density between salt and fresh water involves placing salt water on the bottom half of a glass. The top half of the glass is then filled with fresh water. When an egg is lowered into this water, it sinks through the fresh water and floats in the middle of the glass. This is because it is easier for objects to float on top of denser water.