The WEI+ has been estimated as the quarterly average per river basin district, for the years 1990-2015, as defined in the European catchments and rivers network system (ECRINS). The ECRINS delineation of river basin districts differs slightly from that defined by Member States under the Water Framework Directive. The Ecrins delineation is used instead of WFD because it contains geo-spatial information on Europe’s hydrographical systems with full topological information enabling flow estimation between upstream and downstream basins, as well as integration of economic data collected at NUTS or country level. In addition to using e WISE SoE – Water quantity database, a comprehensive manual data collection was performed by accessing all open sources (Eurostat, OECD, FAO) including national statistical offices of the countries. This was done because of the temporal and spatial gaps in the data on water abstraction. Moreover, a large part of the stream flow data from LISFLOOD has also been substantially updated by the Directorate-General Joint Research Centre. Similarly, a comprehensive update with climatic parameters has been performed by the EEA based on the E-OBS dataset.

see https://www.eea.europa.eu/data-and-maps/indicators/use-of-freshwater-resources-2/assessment-3