This paper presents a methodology based on the ISO-50001 standard to assess the energy impact of replacing standard-efficiency motors with high-efficiency motors driven by variable speed drives in an industrial pumping system.The methodology includes the inspection and installation of the new technology, measurements, data processing, and analysis of the results.In addition, an energy efficiency indicator, an energy baseline, and a Pareto diagram are used, while the harmonics generated by new technologies are evaluated.The contribution of the methodology is that it allows for a comprehensive energy diagnosis using easily measurable data like electricity consumption and water flow, replacing the measurement of the motor's mechanical power in industrial conditions, which is a current challenge.The methodology applied in the case study showed that the technological changes saved 36% of energy and that the variable speed drives increased current harmonics by 10%.