This book presents new approach of process design and cost(Thermoeconomic) model of water desalination plants including MSF, MED, RO and Hybrid technologies. The model is developed to perform stream calculations of mass, energy, entropy, exergy and cost of the desalination plant. This model enables to determine the desalinated water cost and to find out the defficient unit in the overall plant. This book presents a flexible Visual Design (VDS) software for process design and cost calculation of desalination plants which is developed by the author. The developed VDS enables to evaluate the existing desalination plants performance and design new configurations as well. The developed VDS offers a great help not only to the designers and process operation engineers but also to the researchers and students. This book also presents the commercial desalination tecnholgies and market trends that meet the customer/public requirements. Technoeconomic of typical desalination plants are presented. Possible hybrid thermal/membrane technologies are simulated. Finally the capability to develop economically and environmentally accepted desalination project is presented.