This paper explores some of the basic thermodynamic and technical considerations involved in using water as a working fluid for refrigeration and heat pump cycles down to its freezing point of 0-degrees-C. It is first shown how the integration of the functions of refrigerant and heat transfer fluid can lead to energy savings, especially for the case of ice production. Next, the two fundamental requirements that the compressor must fulfill-handling a very large volume flow and achieving a large compression ratio-are described. A thermodynamic analysis of multistage compression follows to investigate the adiabatic head requirements and the large desuper-heating irreversibility. It is concluded that a radically new type of vacuum compressor must be developed in order for water to be used as working fluid in vapor compression refrigeration cycles.