Water, after oxygen, is the second most important substance for human health. Water is a universal solvent and transport medium, and because of that it is the basis of all biological processes in the human body.
Water is mainly important for the digestive system, because it contributes to the constant supply and export of products and substances. The transport of nutrients can only take place through a solvent, and as such water acts as the main transport medium of nutrients.
Water also attends heat regulation in our bodies. For humans it is of vital importance that the body temperature stays at a standard level. That is why we have to drink water, when we are infected with a fever. Water takes up heat and transports it out of the body while we are transpiring.
We can survive without food for about 30 to 40 days, but we can only survive a few days without water. This is a factor that proves how important water is for us.