For the last 20 years, ERSAR has been using a system of key performance indicators (KPI) to compare all operators in terms of their quality of service. This set of indicators was designed to be applicable to every operator, regardless of their sophistication level and should provide generic information for regulatory purposes, but also to support each operator in improving to achieve a good quality of service. More recently, for the bulk operators, ERSAR has introduced in its economic regulation model efficiency metrics and reference costs to signal the efficiency levels operators should achieve in specific KPI and which were the basis for adjustments in tariffs. ERSAR is now working in an evolution of this model which applies a Data Envelopment Analysis considering multiple variables to assess the efficiency levels of each operator. These efficient costs levels will provide incentives for operators to aim for additional savings in operational costs with the purpose of ensuring adequate tariffs to consumers in an efficient context.