Life on Earth has an intimate relationship with water. All organisms, from humans to bacteria, are primarily composed of water; it is the main component of our cells, and most of our tissues and organs are bathed in it. It is through water that nutrients, vitamins and hormones are delivered to different parts of the body where they are used for producing energy and carrying out life’s basic functions. Different environments place strong demands on water use and, as such, animals exhibit many diverse adaptations for collection and conservation of water and protection from being exposed to too much water. On one extreme, organisms in harsh environments like the desert struggle to acquire enough water to survive, while on the other extreme aquatic organisms are surrounded by water and must prevent their tissues from becoming overcome by it. While different organisms have different relationships with water, maintaining a balance of water within the body is crucial for survival.