From the nestle corporate website:
The body fluids contained in the different compartments perform the following important functions:
· Carry nutrients and waste products.
· Vital to the life and shape of every cell.
· Participate actively in many important biochemical reactions of digestion and metabolism.
· Assist with temperature regulation, i.e., cooling the body by evaporation from the skin as perspiration (sweating).
· Act as a lubricant around joints.
· Serve as a shock absorber, e.g., for the brain and the spinal cord or inside the eyes; in pregnancy, the amniotic fluid around the growing foetus provides protection against shock.
· Serve as a solvent for minerals, vitamins, amino acids, glucose and many other small molecules.
There's more on the subject of water at the above link. It's very brief, but it's pretty good.