Liquid water is essential for the existence of living organisms. All cells contain water. The chemical reactions that sustain life occur inside water solutions. 

Life on Earth first emerged in saline ocean water. However, as life moved to land, the importance of water for living organisms did not decrease at all.

All cells require water to sustain their vital functions. Only a few plants or animals can survive for long periods of time without water. The seed of a plant is an example of a resting form that is capable of surviving without water for a long period of time. In water environments, the changes in temperature are slower than they are on land. The specific heat capacity of water is high. This means that a lot of thermal energy can be bound into water molecules. 

The thermal conductivity of water is also quite good. This means that water conducts heat very efficiently. Humans can dwell outside without protective equipment when the air temperature is at 10 degrees Celsius, but would quickly catch a cold when dwelling in water of the same temperature. Because of the thermal qualities of water, shore areas have different climate conditions compared to inland environments. For example, winter arrives later to sea shores than it does to inland areas.

For a plant growing in a water environment, the amount of water is not a restricting factor. On the other hand, water environments provide less oxygen and nutrients than land environments. Freezing and salinity also provide challenges for organisms that live in water environments. A frozen ice layer prevents light from entering the water and reduces its oxygen concentration.

Qualities of water:

• To warm up a kilogram of iron from room temperature to 100 degrees Celsius requires approximately ten times less energy than warming up a equivalent amount of water to its boiling point.
• When water cools down, it releases energy to its environment.
• The freezing/melting point of pure water is 0 °C. The boiling point of water is 100 °C.

Water is the basis of life.