Introduction We all know water is essential for life. We also know that many people – too many – are not getting enough of it, both quantity and quality, that allow them to live healthy lives. And for many of the world’s poor, access to clean water is too costly. For some countries, the percentage of people lacking adequate water supplies exceeds well over half of their total populations. As a result, many, especially the very young, die. Others are constantly sick and, hence, cannot achieve their full productive potential (UNESCO 2003, 2009). So, the question is just how can we “optimize water for life,” especially in areas lacking enough water to satisfy even life’s basic needs? How do we make decisions on how much water to allocate to each of the many beneficial uses of water in times of water stress? In addition to drinking water, people need food and clothing, and the production of the world’s food and fiber requires water. There is nothing we eat or wear that does not depend on water. The production of energy, either thermal (including nuclear) or hydropower, requires water. The materials in the buildings we live and work in, and their contents, require water for their manufacture. Water also serves as an inexpensive means for transporting cargo and water-borne wastes. And, very importantly, we need water to maintain viable and diverse ecosystems. We depend upon our environment and ecosystems to sustain the quality of our lives, and indeed life itself (Postel et al. 1996; Fischlin 2007). In the past decade, progress has been made in providing more people with access to clean drinking water and basic sanitation (UNESCO 2009). But a major effort is still required to extend these essential conditions to those still without them, the vast majority of whom are poor and cannot pay the costs of these basic services. In addition, we are increasingly recognizing that we humans will not easily survive in the long run, unless we pay attention to maintaining a quality environment and life-supporting ecosystems. Again, water is needed to do this, and in times of drought determining the “optimal” allocations of water to sustain our lives, our economic activities, and our ecosystems is indeed a challenging economic and social endeavor (see, for example, Doyle and Drew 2008).