Investigating water sustainability towards indicators: An empirical illustration using country-level data

This paper contributes to the academic debate on the construction of synthetic indices with respect to water-based sustainability analysis. In this regard, the United Nations Sustainable Development Goal (SDG) 6.4 specifically considers the progress on water-use efficiency within the target of ensuring access to water and sanitation (SDG 6). Our contribution investigates the levels of water sustainability reached by countries around the world considering a suitable measure of the goal obtained by aggregating variables available at the national level, i.e. water efficiency (SDG 6.4.1) and stress (SDG 6.4.2). The construction of a composite index for SDG 6.4 is discussed through the usual steps of normalization, aggregation, and weighting, also highlighting the pros, cons and issues encountered in each step. Fundamental issues faced in the construction of synthetic indices are also discussed: different methods for performing the above steps are compared, and uncertainty analysis is carried out to understand which methods could be reasonably suitable to measure the synthetic indicator of the entire target. As a further theoretical contribution, we illustrate some arguments in favor of the application of categorical scales for normalization, even if the results of some countries seem to be particularly sensitive to the choice of weights in the aggregation phase. Results, obtained after examining univariate and multivariate descriptive statistics, show that the best performances can be observed in small and medium Eu- ropean countries and sub-Saharan African nations (such as Congo, Gabon, and Angola), while the lowest levels appear to be located in Central Asia, the Middle East, and North Africa. A natural implication of this research is its contribution to valorizing the social capital of a regional area, stimulating new approaches to environmental issues, informing public debate, and influencing policy-making.