"Water has no taste, no color, no odor; it cannot be defined, art relished while ever mysterious. Not necessary to life, but rather life itself. It fills us with a gratification that exceeds the delight of the senses." - Antoine De Saint-Exupery. Antoine is correct. Water is not necessary for life, it is life. Water was extremely important in the ancient world. It was used to drink, irrigate crops, and to cook with. Without water, a society would be nonexsistent. For example, if the Mayans did not have access to water, their entire advanced civilization would have collapsed. If you were to look on a map it would be obvious that every major city or metropolitan area is located near water. If evidence of water is found on a foreign planet or extraterrestrial place it shows that life may have been supported or that the place is supporting life.
Image from: http://commons.wikimedia.org/wiki/File:2006-01-28_Drop-impact.jpg
Quote by: Antoine De Saint-Exupery (1900-1944), Wind, Sand, and Stars, 1939.