Solar-powered water pumping is an inherently sensible proposition due to the pump being able to supply water at times when it is most in demand. In general small solar-thermal water pumps hold some promise for low technology applications in developing countries. The aim of this study was to model the characteristics of an appropriate technology water pump and build a concept-proving pump. A detailed computer model of the pump and flat plate collector gave the ability to optimise the pump's dimensions and predict the output for any average day in any location. An exergy analysis showed that the major losses in the system were due to wasteful processes within the pump's operating cycle. The pump took the form of a 450mm diameter double diaphragm suction unit with a predicted operating efficiency of approximately 1% when operating at 68°C. The concept-proving pump was set up using compressed air and preliminary runs on pentane gave an efficiency of 0.3%. The pump takes water from 7 metres below to 1.5 metres above the pump at a rate of 3 litres every 10 seconds. A financial analysis highlighted the fact that the solar pump has higher capital but lower running costs than some of its competitors, and as such would suit certain niche applications. Recommendations are to improve the physical lay-out of the pump and improve the design of several components to enable better performance of the pump operating on the same principle.