The story of the most abundant substance on Earth, from its origins in the birth of stars billions of years ago to its importance in the living world.Water is so ubiquitous in our lives that it is easy to take for granted. The average American uses ninety gallons of water a day; nearly every liquid we encounter is mostly water--milk, for example, is 87 percent water. Clouds and ice--water in other forms--affect our climate. Water is the most abundant substance on Earth, and t