Water must gain or lose a relatively large amount of energy for its temperature to change. As heat is added to water, most of the energy is used to break the polar bonds holding water molecules to each other. Only after these bonds have been broken can the individual molecules begin to move faster, increasing the temperature. This characteristic of water helps living things maintain homeostasis - a stable level of internal conditions. All living things need energy to survive.
Energy is defined as the ability to do work or cause change.
Within any living system, it is the free energy that is important. Free energy is available to fuel the cell processes of living things. All living things need a constant flow of energy into and through their systems. Many of the chemical reactions that transfer energy in living things involve the transfer of electrons. These reactions occur most easily in the polar enviornment of a water solution.