Without energy and water, we cannot satisfy basic human needs, produce food for a rapidly growing population or achieve economic growth. Water–Energy Nexus deals with the efficient integration of water and energy resources in order to tackle a wide range of design, operation and optimization issues for systems including both of these two resources. Many problems such as the supply and the continuous availability of the resources, their quality and safety, the environmental and social impacts, along with the cost and/or profit emerged from their exploitation, are problems encountered in a very wide range of real situations. Food is in most cases involved due to its strong interaction with the other two utilities. The course has the intention of analyze the strict relationship between water and energy. In our modern society, a large quantity of water is used for energy production, including both electricity and sources of fuel including oil and natural gas. In parallel, energy is consumed to extract and purify materials, deliver, heat/cool, etc. Moreover, energy is consumed also to treat and dispose water (and wastewater) and to purify drinking water. Water-Energy Nexus is not truly a closed loop as the water used for energy production need not be the same water that is processed using that energy. In turn, all the forms of energy production require some input of water making the relationship inextricable. However, both water and energy are within a delicate equilibrium which need to undergo a sustainable approach. Sustainable utilization of water and energy and their interconnection will be highlighted and discussed.