Water is the liquid of life and is crucial to every type of organism, from simple bacteria to megafauna, as well as to many of the physical processes that shape the planet, as in the weathering of mountains and valleys. For life in all forms, water is more important than even oxygen, because there exist anaerobic bacteria that can live without air but no anhydroxic bacteria that can exist without water. When astrobiologists seek to determine the possibility of life on other planets, their first question concerns the presence of water. Throughout human history, however, water has had as much a symbolic as biological significance, and human beings have adapted to environments both abundant and scarce in water, through different technological, ethical, and political engagements. Water is so rich in metaphor that it cannot be reduced to merely H₂O, nor to a fluid circulated in pipes, metered...