Accessibility to water and energy in sufficient quantity and quality are essential for human development. Hence provision of both these commodities accounting for their sustainable use and the need to mitigate global climate change by reducing greenhouse gas emissions are primary tasks of the 21st century. Increasing stress on water resources, and the need to better assess ‘clean’ energy resources such as geothermal energy, require the development and application of sophisticated, state-of-the art tools such as numerical modeling. To illustrate this present-day world concern, we will start this introductory chapter with some information, mostly from the UN organizations on the global water problem and from the Intergovernmental Panel on Climate Change about the process of global warming related to the energy issue and cite their most important findings (sections 1.1 and 1.2). These reports highlight the importance of better addressing these issues guaranteeing the development and survival of humanity.