In the present database we propose a differentiation between the uWF of production (uWFp) and the uWF of supply (uWFs) of primary and processed crops. The uWFp refers to locally-produced crops whose water footprint depends on the crop actual evapotranspiration and crop yield, with values which are here estimated annually starting from 1961. The uWFs refers to the domestic supply of primary crops, which relies both on local production and on international trade. Domestic supply is used as human consumption, food manufacturing, feed for livestock and as export towards other countries. The impossibility to track local production and imports into consumption and exports, within each country, makes the uWFs the best indicator to be used in conjunction with consumption and export data. The uWFs of primary crops is computed averaging local production and imports, after identifying the countries of origin of the goods thanks to an appropriate procedure applicable from 1986.
Processed crops are produced from a root product which may or may not originate from local production. The absence of systematic FAO data about the production of processed crops prevents the differentiation between the unit water footprint of production and of supply. Therefore, processed crops considered in this study will have a single unit water footprint, depending on country and year, computed applying some conversion factors to the uWFs of the root product. Finally, animal-based products are here considered only with the WaterStat values, without temporal variability.