Life on Earth relies on carbon chemistry, with water as a solvent, not by accident, but because carbon and water have an inherent superiority. Water remains liquid within a large range of temperatures. Water helps organism that contain it to regulate their temperatures. It has the ability to dissolve other chemical compounds, to transport nutrients and to carry off wastes.
Many metabolic reactions require water as a reactant.
The very shape and internal structure of cells depends on it. Biologists believe that life originated in water. Many organisms still live in it, and the ones that don't carry water around with them, in cells and tissue spaces.