Salt serves a variety of functions in the human body. Some of the biological machinery in the body needs salt to function. One example of this is the cellular "pumps" which move various things into and out of a cell. Sometimes these pumps are used to send messages between cells. These pumps often require salt to function.

In addition, one of the ways that the body knows whether to drink more water or urinate is based on how much salt is in the blood. If there is too much salt in your body, you get thirsty so that you drink more water and dilute the salt. Salt is in fact so important, that humans and animals in general are really good at sensing salt in food as a "salty" flavor.

Another way to view the role of salt is in keeping your cells the right size. Your cells naturally have salt in them as does the surrounding blood. If you put a cell in water that is too salty, water will flow out of the cell and it will shrivel. However, if you put a cell in water that is not salty enough, water will flow into the cell and it will swell and burst. This process is called "osmosis" which describes how water tends to flow from dilute solutions into more concentrated solutions.