Of the water on Earth, 97% is salt water and is stored in seas and oceans. As its name implies, salt water contains a large amount of sodium chloride (common table salt). This means that only 3% of water on Earth is fresh! Of this, most is locked up in icebergs and glaciers and inaccessible for human use. This leaves less than 1% of the water of Earth for people, plants, and animals to use.
Water makes up the majority of the fundamental substance (protoplasm) of which animal and plant bodies are made. The sap of plants and blood of animals contain large quantities of water. Water is essential to the manufacture of starch by plants.
Water and the Human Body
Approximately 66% of the human body consists of water. Our organs contain water and it is transported throughout our body to help perform physical functions. . A person can live about a month without food, but only about a week without water. Dehydration results if a human does not absorb enough water. Many foods, such as milk and fruit, have high water content.
Water as a source of power is of major economic importance. Water is used to directly do work or via a turbine to generate electricity. Many large dams generate significant electricity around the world.