The IAEA DEEP software has been used worldwide for the economic evaluation of desalination plants (thermal or electrical) coupled with various energy sources (nuclear, fossil fueled or renewable). Throughout the years, the software was updated constantly. Such updates included the user interface and model structure but not the economic models. Previous continuous development was culminated in the development of the DEEP 3.2 version which has been recently released in 2009. This paper presents a step forwards in the continuous effort to maintain high standards and reliability of DEEP. It also scrutinizes methods used, assumptions made, and constants or default values originally used. The validity of calculations as well as the identification of the most important parameters is presented. Sensitivity analysis is used to identify the most important parameters in the DEEP model. Overall, the review proves that both the DEEP economic model and software implementation are solid for economic evaluation of dual purpose plants. Based on results presented and recommendations made, a new version of DEEP is expected to be released in 2010 which will address minor issues and improvements.