**4. Conclusions**

Despite the multiple benefits brought by following an e fficient performance, in water managemen<sup>t</sup> only a few works provide alternatives. In this context, benchmarking plays an important role. Normally, to study the e fficiency requires information collected by indicators. However, some di fficulties arise when dealing with several indicators and their interpretation. In order to overcome these problems, CIs are introduced in this field, providing di fferent strategies to aggregate the indicators into a unique score that summarizes the information.

In particular, this work provides an alternative methodology to evaluate the performance of a set of Portuguese water companies following two steps. First, in order to analyse the economic, social and environmental dimensions, we divide the initial set of indicators into these three dimensions and construct a partial sustainable index for each of them, inspired by GP. In general, water companies present the largest value for the economic partial sustainability indicator (PSUIEC), whereas the partial sustainable index for the social and environmental dimensions present poor scores, the former being slightly lower. In particular, ranking these results, we find that just a few water companies stand out among the top 20 best scores in the three dimensions, simultaneously. This fact could be translated into policies to improve social and environmental aspects of the water companies. The second step uses a variant of DEA to provide a global performance index that uses the information provided by the partial indicators for each company. As a result, a large percentage of water companies obtain a global score over 0.7, whereas no companies show a value below 0.2. However, an individual analysis of the contribution of each dimension to the global score shows no equilibrium.

Furthermore, in this analysis one may observe two profiles: on the one hand, many water companies present a good global score due to the value they achieve in the economic partial sustainability indicator, whereas, on the other hand, the good global results of the other companies are due to their performance in the social and environmental dimensions, jointly. The results obtained show that the water companies, in the Portuguese context, do not manage their activity in a balanced way from the social, environmental, and economic point of view. Consequently, there are no water companies, in this context, that can be considered a "good benchmark" for the rest, so that they achieved good results in the three dimensions in a balanced way. In this case, each water company should seek to improve their results in the dimension(s) with lower contribution in the sustainability, taking into account the scores in the first phase, without neglecting the maintenance of good performance in those dimensions in which good results are obtained. In this context, as a future line of research, it would be interesting to define an ideal company that reaches a good percentage contribution of each dimension on the sustainability, and then compare the sample of water companies with this one ideal.

Nevertheless, this work introduces an alternative to assess the sustainability of water companies in two phases. It permits assessing and/or comparing the dimensional sustainability in the first phase, and to provide a holistic performance perspective in the second phase, generating a ranking of the water companies. The proposed approach could be very useful for water regulators: (a) to verify the effectiveness of existing policies; (b) to support decision making in concrete dimensions; and (c) to monitor global trends. In other words, measuring sustainability, holistically and for dimension, will allow water regulators to make critical decisions and, if needed, implement corrective measures to improve it and do it in the correct direction.

**Author Contributions:** All authors contributed to the paper as follows. Conceptualization, F.P., L.D.-A. and T.G.; Methodology, F.P., L.D.-A. and T.G.; Software, F.P.; Validation, F.P., L.D.-A. and T.G.; Formal Analysis, F.P., L.D.-A. and T.G.; Investigation, L.D.-A.; Resources, F.P., L.D.-A. and T.G.; Data Curation T.G.; Writing—Original Draft Preparation, F.P., L.D.-A. and T.G.; Writing—Review and Editing, F.P., L.D.-A. and T.G.; Visualization, F.P., L.D.-A. and T.G.; Supervision, F.P., L.D.-A. and T.G.

**Funding:** This research was funded by Ministerio de Ciencia, Innovación y Universidades from Spain, gran<sup>t</sup> number ECO2016-76567-C4-4-R; by the Consejería de Conocimiento, Investigación y Universidad from Junta de Andalucia [SEJ417] and by Universidad de Málaga, gran<sup>t</sup> number PPIT.UMA.B1.2017.21.

**Conflicts of Interest:** The authors declare no conflict of interest.
