Water Efficiency Targets at the Basin Scale: Useful Guide or Policy Trap?

Abstract Relevant EU water policy documents, such as the EU Blueprint for Water report (EC 2012) and the European Water Resilience Strategy (EC 2025) call for the development of basin-specific water-use efficiency targets, emphasising the importance of considering the broader impact of individual measures at the river basin level. This study contributes to the discussion on the suitability of basin-wide water-use efficiency targets to guide and inform water policy with the goal of achieving environmental objectives (as those set by the EU Water Framework Directive). The novelty of this study lies in the application of a hydro-economic model, calibrated with real data, to assess how local water-use efficiency improvements translate to basin-scale outcomes. The case of the Guadalquivir River Basin (southern Spain) shows that increases in on-farm efficiency do not necessarily generate basin-wide water savings. This is largely due to the reuse of return flows and the hydrological interdependence between upstream and downstream users, which limit the net reduction in water consumption at the basin level. Our study emphasizes the fact that targeting basin-wide water-use efficiency is a complex issue affected by multiple aspects (e.g., environmental, socio-economic, legal, technical, and political), which significantly limit its usefulness to make comparisons between river basins (or districts) and guide water policy.