Figure is from Hanasaki and others paper An estimation of global virtual water flow and sources of water withdrawal for major crops and livestock products using a global hydrological model (2009 Journal of Hydrology) doi:10.1016/j.jhydrol.2009.09.028.
They explain the figure:
The estimated flows of virtual water exports and imports in 2000 by nation were aggregated into 22 regions worldwide (Table 9; Fig. 4) to show net exports between regions.
Fig. 4a shows the virtual water export flows for all water sources. The figure indicates that North and South America were major regions from which virtual water export flows originate; East Asia, Europe, Central America, and West Asia were the major destinations. This pattern of flows agrees with the studies of (Oki and Kanae, 2004), (Yang et al., 2006) and (Hoekstra and Hung, 2005).
Fig. 4b shows the virtual water exports of blue water (withdrawn from streamflow, medium-size reservoirs, and NNBW sources), and
Fig. 4c shows the virtual water exports of NNBW. Most major flows of blue water and NNBW originated from North America and South Asia.
Interestingly, South America was the major total virtual water exporter but a minor blue water exporter because less cropland is irrigated on this continent.
Notably, South Asia, which is densely populated and where demand results in water scarcity (Oki and Kanae, 2006 and Hanasaki et al., 2008b), showed blue and NNBW virtual water export flows. [note: NNBW – is non-renewable and non-local blue water.]