Exergy Analysis has been identified in the literature as a powerful tool to benchmark the resource efficiency of thermal systems. The exergy approach provides a rational basis for process optimisation, where, in theory, the processes with the greatest exergy destruction represent the greatest energy efficiency opportunities. Exergy analysis of a Waste Water Treatment Plant (WWTP) has been performed. In addition, two separate reference environments for WWTPs are defined based on plant location. Biological oxygen demand was identified as the most useful parameter when calculating the chemical exergy of organic matter in waste water. The results of this study indicate that organic matter is the principal contributor to chemical exergy values and that exergy analysis is a useful approach to identify inefficient processes within a WWTP.