One third of the world population does not have access to clean water sources and most of these people are not connected to the electrical grid at the same time. Therefore, photovoltaic (PV) powered water purification suggests itself to be one of the solutions in areas with high sun radiation like India or the MENA (Middle East and North Africa) region. Furthermore, the environmental impact of the process can be reduced substantially as no fuel supply is required. The paper presents a concept of combining a membrane filtration plant with PV power supply only. As PV is. a fluctuating energy source and the conventional membrane process needs a constant power input to maintain pressure and flow on the membranes to guarantee their lifetime, some challenges in the system design need to be addressed. Mere coupling of off-the-shelf components does not do the job. A full-scale system for sustainable water purification has been designed and tested in the lab and a pilot location. The results are presented in the paper. Beyond the environmental benefits, the system also competes with standard systems on the market. Based on the experimental results, a cost model has been derived, the main cost factors for the system will be established and a design strategy for a small-scale PV powered system, able to supply a farm or village with safe potable water, is presented.