In thinly populated and regions a frequently emerging task is the pre-design and pre-evaluation of desalination plants for small scale applications: the supply of potable water to remote villages or the back-up of unreliable public water services by local means. A computational tool was developed to achieve a pre-selection of appropriate systems from the wide range of technologies available nowadays, including those suitable for the use of energy from renewable sources. The procedure starts from source data on the local climatic, technical and socio-economic conditions and delivers key results on design parameters, technical performance and costs. The results are used to lay a save ground for the detailed decisions on the feasibility and on the concept for the project development.