A solar system for disinfection of water, to be applied in developing countries and/or long-term emergencies is presented. The system uses commercial solar thermal collectors arranged in a self compensating natural circulation system, using no electricity and sized for adequate residence time for disinfection by pasteurization. The basic rules for circuit design/sizing are explained, and a time dependent off-design model is applied to evaluate the daily and seasonal productivity in different example locations. The discussion includes an exergy analysis of the system and the definition and assessment of performance indicators. The proposed system is simulated in different locations, demonstrating the capability of producing typically from 40 to 80 kg/day per m(2) of collector surface depending on the location; the performance is compared to a Reverse Osmosis/Photovoltaic system, representing a high-tech alternative for the purpose of water purification. (C) 2017 Elsevier Ltd. All rights reserved.