The raster dataset of easily available water has a spatial resolution of 5 * 5 arc minutes and is in geographic projection. Information with regard to available water was obtained from the "Derived Soil Properties" of the FAO-UNESCO Soil Map of the World which contains raster information on soil properties.

This map, compiled to support the analysis of SOLAW report concerning trends and current use of water use in agriculture, shows the percentage of irrigated area supplied by groundwater. Irrigation mainly relies on renewable freshwater resources, either surface water or groundwater. However, while the extent of irrigation and related water uses are reported in statistical databases or by model simulations, information on the source of irrigation water is still very rare. A recent global inventory undertaken by FAO and the University of Bonn reports that 113 million ha, or 38 percent of the total area equipped for irrigation of 301 million ha, is irrigated by groundwater (Siebert et al, 2010).