The Water Exploitation Index (WEI) was introduced by the European Environment Agency (EEA) and presents the annual total fresh water abstraction in a country as a percentage of its long term average of available water. The WEI shows the abstraction of surface and groundwater divided by the average long term gross outflow from a country (basic WEI) or divided by gross outflow within a year (annual WEI+).

The data on water extraction is obtained from the Statistical Office of the Republic of Slovenia and excludes water used for hydropower generation in Slovenia. It includes water consumption for the public water supply provided to the population, industrial withdrawal, irrigation, etc., and water required for the operation of thermal power plants and the nuclear power plant.

The data on gross outflow from the country is obtained from the Slovenian Environment Agency as an annual river balance based on the river discharge data. In order to estimate the vulnerability of individual river basins in terms of water quantity in the future, an analysis of the monthly WEI, based on the monthly mGROWA-SI water balance, will be required.