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The historical beginning of understanding the importance of water to life started with the Ionic Philosophers (from the Ionic Sea), who began to think that physiology (referring to nature, from the ancient Greek physis ¼ nature; logos ¼ talk) could explain life better than theology (referring to god, from the ancient Greek theos ¼ god; logos ¼ talk). Among these, Talete (624–547 BC) is credited with the observation that he ‘‘principle of nature is water,’’ and all life begins with water. In this essay, we explain how water moves through plants and is used for growth by recounting the history of ideas, observations, and experimentation that form our present basis of understanding of plant water homeostasis. We briefly summarize the history of approaches and discoveries that have identified the growing collection of genes that control altered growth and/or altered water use properties of plants during osmotic mediated stresses, with the exception of freezing stress. These genes, which have often been identified by forward genetic mutation screens, impact one or more of several mechanisms controlling water absorption, movement, and use. A better understanding of the basis of water homeostasis should be a useful tool in the arsenal of molecular geneticists, and increased awareness of the utility of genetics to understand adaptation to osmotic stress should be a great benefit to physiologists.