This article is based on Chapter 17, “Stocks, Flows and Prospects of Water” of an upcoming book: Linkages of Sustainability, edited by Thomas E. Graedel and Ester van der Voet (2010) and published by Massachussetts Institute of Technology Press. You can find the full list of authors by downloading the chapter from the link above. This book catalogues the results of the Ernst Strüngmann Forum (http://fias.uni-frankfurt.de/esforum/), which was convened in Frankfurt in 2008.