The indicator presents i) the annual total fresh water abstraction in a country as a percentage of its long term average available water (LTAA) from renewable fresh water resources; ii) the annual groundwater abstraction as a percentage of the country’s long-term annual average groundwater available for abstraction; and iii) the annual surface water abstraction as a percentage of the country’s long-term annual average surface water resources available for abstraction. The latter is calculated as the total fresh water resources (external inflow plus precipitation less evapotranspiration) less groundwater available for abstraction. Total fresh water abstraction includes water removed from any fresh water source, either permanently or temporarily. Mine water and drainage water as well as water abstractions from precipitation are included, whereas water used for hydroelectricity generation (in situ use) is excluded. The minimum period taken into account for the calculation of long term annual averages (LTAA) is 20 years. The warning threshold of 20% for this indicator distinguishes a non-stressed from a water scarce region, with severe scarcity occurring where the WEI exceeds 40%. However the indicator is limited for several reasons: Firstly, the total fresh water abstraction does not distinguish between abstracted water that is redirected after use (and after appropriate treatment) back to the water body or if it is used for irrigation purposes with inevitable evaporation. Secondly, the abstraction and WEI are national data and disregard regional and seasonal changing conditions during the course of the year (water bodies/river basins with different level of water scarcity and hot spots in summer time). Eurostat is in maintaining more differentiated data but coverage is not yet considered sufficient. As soon as the more advanced indicator WEI+ is established, it will replace the WEI. More information can be found in Statistics Explained.