Water has many roles in living organisms and life on earth is impossible without it. It makes up between 60% and 95% of the fresh mass of the organisms. In a water molecule, two hydrogen atoms are joined to an oxygen atom by covalent bonds. This makes it a stable molecule. The oxygen nucleus attracts the electrons more than the hydrogen nuclei do. This results in the oxygen atom having a ¥ä- charge and the hydrogen atoms having a ¥ä+ charge. This water molecule is referred to as dipolar due to the uneven charge distribution. 

Water plays a very important role in animals. It maintains the process of homeostasis to maintain the relatively constant temperatures within the body. Water has a high specific heat capacity, indicating that it requires a lot of energy to raise the temperature of 1Kg by 1¢ªC. Also, a lot of heat energy must be lost for the temperature of the same mass of water to fall by 1¢ªC. This is important because it means that sudden changes in the temperature, which may upset metabolic reactions in cells, are avoided. These chemical reactions are allowed to tale place within a narrow temperature range so that rates of reaction are more constant. However, for organisms that live in water, large rapid changes in the temperature of their environment do not occur. When animals sweat, heat energy, from the body is used to evaporate the water in the sweat, cooling us down.

Water is also used as insulation. For example, when a pond freezes, ice forms on the surface, insulating the water below so that aquatic organisms can survive. This is especially important in cold seasons. This is due to water having a maximum density of 4¢ªC.