A metafrontier network DEA approach for water usage efficiency assessment in the light of SDG target 6.4

The efficient use of water must be enhanced and promoted to achieve the Sustainable Development Goal (SDG) 6. Thus, to contribute to the achievement of SDG Target 6.4 and close a research gap in SDGs’ progress, this paper carries out a water usage efficiency analysis of 126 countries leveraging the AQUASTAT database maintained by the Food and Agriculture Organization of the United Nations (FAO), providing information that can help assess and promote the sustainable use and management of water. The methodology uses a conceptual model that considers a Water Withdrawal (WW) stage and a Water Productivity (WP) stage, each one with its own set of variables, designing a customised non-parametric frontier analysis solution that identifies the countries with the best practices and uses them as benchmarks for global efficient water usage. In particular, the proposed approach uses a non-radial Directional Distance Function (DDF) that estimates the inefficiency along the different dimensions, both desirable and undesirable, quantifying potential improvement and computing an efficiency score for each stage and for the whole system. Due to the heterogeneity of the sample, a metafrontier analysis has been carried out. The results indicate that there are significant differences between countries and regions in terms of water usage efficiency. The regions with highest efficiency include Australia, Western and Central Europe and Southern and Eastern Asia, while Central Asia has the lowest. Most of the inefficiency corresponds to the Gross Value Added dimension and the WW stage efficiency is generally higher than that of the WP stage.