WWTPs require energy for various processes such as pumping, aeration, mixing, and biosolids treatment. The energy is mainly used for moving water through the treatment process and providing aeration to promote the growth of microorganisms that break down organic pollutants. The main aim of this paper was to analyze energy consumption in three wastewater treatment plants, with the same treatment process, in accordance with the treated flow, and try to find a relation between these two essential resources, in order to propose improvement measures of manage these systems. As expected, generally, the periods of highest flow of wastewater in the WWTP correspond to energy highest consumption. In this case the KPI (kWh/m3) increased with the volume of treated flow. The energy produced represents a small amount compared to what is needed to the WWTP operation. As expected, the most part of energy consumption is related to biological treatment. By understanding and optimizing the energy-to-water nexus, WWTPs can improve their environmental performance, reduce operational costs, and contribute to a more sustainable water management system.