<p>Identifying service providers with the best performance regarding their main operational indicators is relevant to improve the sustainability of the water sector. It is also critical to determine the corresponding drivers, and understand the interdependences, to enlighten the relevant stakeholders about the best course of action. The energy consumption of the service provider is a major issue, regarding sustainability, both for financial (being one of the largest operating expenses) and environmental (emission of greenhouse gases) reasons. In that regard, a Data Envelopment Analysis—Slacks Based Measure is employed to identify the service providers within the efficiency frontier. Only the efficient providers were considered to determine the main drivers and to model the energy consumption by multilinear regression. The current study identifies the effectively served population and the number of served households as paramount for the estimation of energy consumption at the efficiency frontier in wastewater and drinking water treatment, respectively. Other explanatory factors were also found to be significant, especially regarding normalized (per water intake) energy consumption, including energy certification, wastewater treatment plants typology, mains and sewers grid rehabilitation, wastewater satisfactory treatment, number of septic tanks and drinking water treatment plants and collected water volumes. The proposed methodology can be applied to data from any country to identify the role model SP and the corresponding energy consumption drivers, allowing policy recommendations to be tailored to each specific context.</p>