This paper presents the results of a measured data-based mass flow and balance study in UluPandan Water Reclamation Plant (WRP), the second largest municipal wastewater treatment plant in Singapore. The results are benchmarked against the Strass wastewater treatment plant in Austria, which has achieved energy self-efficiency. The gaps between the two plants have been identified and areas for process improvement in UluPandan WRP, especially those related to energy efficiency, have been proposed. This case study demonstrates that mass flow and balance is an effective tool in improving process performance and the energy efficiency of a municipal wastewater treatment plant.