Water has a high heat capacity. It takes a lot of energy to melt ice and vaporize water. Thus water is the principal heat reservoir on the Earth. The asymmetrical charge distribution on a water molecule makes it very effective in dissolving ionically-bonded materials. It is the closest thing to a universal solvent.
Water is very effective at transporting ions and dissolved nutrients in the human body.
Water is not an effective solvent of organic molecules. Thus we do not dissolve in our own cell fluids. When water freezes, it assumes a very open structure and actually expands. Most materials shrink when they freeze and sink in their liquid phases . If ice sank like most frozen solids, it would accumulate at the bottoms of frozen lakes and seas.