This paper presents the work performed within the project "INTERSUDMED-Pre-feasibility Study for the Integration of RES for Electricity Production in South Mediterranean Countries", of the European Commission＇s JOULE Programme. The decentralized characteristics of renewable energies may play a significant role for power supply in rural areas, were grid electricity is not available. One important application is the use of photovoltaics to drive desalination units in order to solve water scarcity problems. Energy and water signify two resources of outmost importace for developing countries, mainly due to rapidly increasing population and the growing need for upgrading their standard of living to an acceptable one. PVs provide a viable means for decentralized energy and water production in arid areas, which also usually present an abundant solar resource. In this basic engineering design of an autonomous PV - Reverse Osmosis (RO) system able to cover potable and other water needs of a rural community in Marocco is presented. In order to design the system, local conditions have been taken ub account. Among the basic design requirements were standardization of the design of such systems and the development of reliable systems with simplicity of operation, procedures are presented. An economic analysis for the RO and the power supply system is also presented.