Ultra-Pure Water (UPW) is a high energy raw material used in the semiconductor manufacturing industry. However, to date, the production of UPW has received little focus in terms of energy consumption mitigation. Exergy analysis is perhaps the most powerful tool available in the search for industrial energy efficiency. The objective of this research was to develop an approach for the exergy analysis of Semiconductor UPW plants in an effort to characterise energy consumption. However, following an extensive literature review, it became evident that several desalination exergy models were in current use, and it was unclear which model was the most appropriate, presenting a serious challenge to researchers seeking to apply exergy analysis to water purification processes. A detailed study and comparison of two predominant desalination exergy models was undertaken to determine the most appropriate model for UPW and other water purification applications. Neither of these models was deemed suitable due to inappropriate underlying model assumptions. Two potentially suitable exergy calculation models were identified from the broader literature and developed further for UPW applications. A novel method (based on Szargut’s chemical exergy reference environment) was developed to calculate the chemical exergy of electrolytic solutions at non-standard dead state temperatures. It was found that, in general, the chemical exergy of ionic species was sensitive to changes in dead state temperature. The exergy models were applied to a UPW plant in an effort to compare the models and characterise the plant. In general, the exergy destruction rates were similar for the three models, the hot water heat exchanger being the main exception (and also a key source of exergy destruction). Chemical exergy proved vital for the calculation of several process exergetic efficiency values and the assessment of plant exergy losses. Following a detailed assessment of the UPW plant exergy analysis results, the most appropriate model was identified.