A mathematical model for a thermodynamic pump capable of lifting water by temperature difference has been developed. The model has been tested experimentally by designing a pump which had no moving parts. The pump was operated by the temperature difference of a condenser (5-15°C) and a boiler (30-50°C). The pump performance was favourably compared with the model and pump output under these conditions was 0.8 W (when 120 kg/hr water was lifted 2.5 m). The pump efficiency was rather low, however, the main advantage of such a pump is the absence of moving parts and direct contact between water and the working fluid.