Water transport across cell membranes is an essential requirement for the biochemistry of life, yet it took more than two centuries of observations and research before transmembrane water channels termed aquaporins were discovered. For much of this time, it was assumed that water transport occurred either via simple diffusion or in certain instances was powered by active processes. As early as the eighteenth century, it was noted that adult frogs and toads absorb water across their ventral skin when dehydrated and placed in water. A century and a quarter later, it was discovered that the increased absorption of water across the skin could be enhanced by the injection of neurohypophysial extract (pituitrin), which was known to have antidiuretic effects in mammals. These...