COCHE-198; NO. OF PAGES 2 Please cite this article in press as: Sikdar SK, Agrawal R: Editorial overview: Energy and environmental engineering: Energy-water nexus: transition from generic to specific, Curr Opin Chem Eng (2014), http://dx.doi.org/10.1016/j.coche.2014.07.005 Editorial overview: Energy and environmental engineering: Energy-water nexus: transition from generic to specific Subhas K Sikdar and Rakesh Agrawal Current Opinion in Chemical Engineering 2014, 5:xx–yy http://dx.doi.org/10.1016/j.coche.2014.07.005 2211-3398/Published by Elsevier Ltd. Vast amounts of research results and opinion pieces accumulated over the recent past on clean water quality and quantity have brought energy-water nexus to the forefront as an important civil society issue. Various environ- mental, economic, and societal factors are driving this section, such as global warming due to emission of greenhouse gases from energy production, and shrinking clean water reserves resulting from unsustainable water with- drawal, which is turning many parts of human-habited world into water- stressed areas. In simple terms, energy-water nexus means that we need useful energy to produce clean water, especially drinking water, and con- versely we need clean water to produce useful energy for doing work, such as providing electricity or raising steam. Other nexuses derived from this concept are being discussed as well, the most prominent of them being energy-water-agriculture nexus. The inter-connectivity of the appropriate sectors of the economy, once unappreciated, is now considered essential to include into the design and analyses of many anthropogenic enterprises to avoid societal ills that could be explained away before as unintended consequences but are now clearly possible to anticipate and avoid by engineering approaches. Production of energy and water for industrial and civic uses may not have been a central focus of chemical engineering, but this discipline typically employs these resources in various chemical conversion processes that produce industrial and consumer goods, and hence examining the dynamics of the nexus has become a research and operational focus in chemical engineering. We know from thermodynamic principles that the total energy of a system is conserved, yet it is the useful energy, called exergy, that is relevant in this nexus parlance. Similarly, the total water content of the globe is the same regardless of the quality of water, but we are mainly concerned about clean water which can be seen as the equivalent of the exergy concept because it is in that form we can make use of water. This concept of water scarcity in the face of abundance was sharply brought into relief in the immortal words of Samuel Taylor Coleridge in his poem, The Rime of the Ancient Mariner: Water, water, everywhere, And all the boards did shrink; Water, water, everywhere, Nor any drop to drink.’’ In the works of engineers, the energy-water nexus is going beyond the statistics of numbers to mathematical analyses of processes that produce energy or water to the design and operation of plants that make useful Subhas K Sikdar National Risk Management Research Laboratory, US Environmental Protection Agency, Cincinnati, OH 45268, USA e-mail: sikdar.subhas@epa.gov Dr. Subhas K Sikdar is the Associate Director for Science for the National Risk Management Research Laboratory of the U.S. EPA in Cincinnati, OH. For 22 years he championed the concepts and methods for clean products and processes for the Agency and in NATO projects and engineering workshops. He is the founder and the co- Editor-in-Chief of the international journal, Clean Technologies and Environmental Policy. He currently chairs the Engineers’ Forum for Sustainability and has published more than 80 technical papers in reputed journals, has 27 U.S. patents, and has edited 15 books. Rakesh Agrawal School of Chemical Engineering, Purdue University, Forney Hall of Chemical Engineering, 480 Stadium Mall Drive, West Lafayette, IN 47907, USA e-mail: agrawalr@purdue.edu Rakesh Agrawal is Winthrop E. Stone Distinguished Professor, School of Chemical Engineering, Purdue University. A major thrust of his research is related to energy issues and includes novel processes for fabrication of low-cost solar cells, biomass and liquid fuel conversion, and energy systems analysis. His research further includes synthesis of multicomponent separation configurations including distillation, membrane and adsorption based processes, basic and applied research in gas separations, process development, gas liquefaction and cryogenic processes. He is a recipient of the U.S. National Medal of Technology and Innovation. Available online at www.sciencedirect.com ScienceDirect www.sciencedirect.com Current Opinion in Chemical Engineering 2014, 5:1–2