In the last years the demand on fresh water continuously increase worldwide and the future demand is difficult to estimate, but due to the growth of population and the increase of the worldwide demand on consumer goods the water demand will also rise in the close and far future. Furthermore more environmental neutral energy resources are needed to fulfill the needed energy requirements in the future. One option is to use solar thermal energy to produce (process) heat. This paper is about the modeling of a demonstration plant in the Egyptian Sunwater project. The energy from renewable energy source is used to operate a water desalination unit and to produce freshwater environmental friendly. The main heat generator for the water desalination unit are solar thermal panels. The produced freshwater is free of ingredients and it can be used, with the accumulation of trace elements, as normal drinking water. The water desalination module works with evaporation and the whole construction will be installed close to a hotel complex in Egypt as a demonstration plant. It is funded by the EU and the Ministry of Higher Education and Scientific Research in Egypt (RDI). This project is a feasibility study to show the possibility to combine solar thermal energy and a water desalination module working with evaporation. It could be an impulse for future research projects and for a freshwater supply not only in dry and hot countries like in Africa. For the installation of the components at the demonstration plant a system model and a simulation was done to combine the right components at the building site to a sustainable system.