Small-scale decentralised water and power cogeneration systems with hybrid renewable and fossil power and process heat supply must not only exhibit a technically sound design, but the chosen configuration must also be economically viable. The availability of competing technical solutions to generate the commodities drinking water and electricity in combination with the uncertainty related with the prediction of future scenarios necessitates the transparent and computer-aided comparison of different options. This paper describes the basic features of the simulation environment IPSEpro and how it was adapted to allow for the specific needs of feasibility assessment studies on de-central water and power supply integrating renewable energy in MENA countries. IPSEpro is an open framework for process modelling and consists out of several modules for specific purposes. The basic modules are the Process Simulation Environment (PSE) and the Model Development Kit (MDK). They are used for building and solving process models and for defining new component models, respectively. PSEconomy is an extension module for the techno-economic analysis of processes and allows detailed evaluation of life cycle cost for different technical process configurations under varying economic scenarios. The process specific technical and economic details are contained in so-called model libraries which are created and extended with MDK. With this approach it is possible for end-users to develop very detailed but still adaptable solutions without the need to get into time-consuming high-level programming. The special model library RESYSproDESAL covers a wide range of technologies for energy conversion and sea- and brackish water desalination with emphasis on energy supply from renewable sources. Cost data are allocated to system components contained in the library as functions of size and capacity. They are based on market information, and cost parameters as well as functional relationships can be updated at any time. The economic assessment is performed through a complete through-life cycle cost analysis, which includes the total capital cost of the plant, the cost of fuel, O&M costs and the expected revenues from the sale of power and water at different operating conditions. Varying economic scenarios, including anticipated inflation and fluctuations in fuel prices and product revenues, can be taken into account. PSEconomy generates different profitability measures like net present value (NPV), internal rate of return (IRR) and product through-life costs, which can be used for economic assessment. The capabilities of the software are illustrated by an exemplary case study based on RESYSproDESAL models.