This dissertation was written as a part of the MSc in Energy Systems at the International Hellenic University. It examines the interconnection between water and energy in both ways at an international level, and tries to proceed with exact numerical results for the whole energy-water system in Greece. In addition, measures for the improvement of water use efficiency are described. At this point, I would like to thank my supervisor, Dr Theodoros Zachariadis for providing me with the opportunity to deal with such an interesting scientific area. In order to successfully complete this Msc programme, I was financially and ethically supported by IKY FELLOWSHIPS OF EXCELLENCE FOR POSTGRADUATE STUDIES IN GREECE - SIEMENS PROGRAM, to which I am grateful.
