A water molecule consists of two hydrogen atoms and one oxygen atom. A water molecule has an angular shape. Due to the high electronegativity of oxygen, the water molecule is a dipole. As a result, the part of the molecule where hydrogen is located is positively charged, and the part where oxygen is located is negatively charged. This leads to the formation of multiple hydrogen bonds between water molecules. The specific structure of a water molecule determines specific characteristics of water and its functions in the living organisms. As a water molecule is a dipole, water is a good solvent and serves as an environment where all enzymatic reactions occur. Water is a reagent in hydrolysis reactions. Water has good thermal conductivity and high heat capacity making it a perfect substance to conduct and maintain heat in the body. Water slowly heats up and cools. Water is characterized by the optimum surface tension force for biological systems. The maximum density of water at 4° C is 1 g/cm3. As a result, ice has a lower density and floats on the water surface. Therefore, water masses do not freeze in winter allowing the survival of organisms.