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Fresh water is a scarce resource on a worldwide basis. This becomes apparent when looking at the basic items of the global freshwater balance. Of the 110,000 km(3)/a of precipitation on the landmass of the earth, 50,000 are returned to the atmosphere via evapotranspiration by the planet's natural plant cover. Another 21,000 are used by man-made ecosystems (18,000 km(3)/a by rain fed agriculture and 3,000 km(3)/a by irrigated agriculture). This shows that agriculture and natural vegetation are already fierce competitors for the available freshwater. Of the accessible runoff of 13,000 km(3)/a about 4,000 are appropriated by mankind. 70% of those go into irrigated agriculture. This means that a global water crisis would above all be a global crisis in food production. Compared to the 13,000 km(3)/a available the abstracted 4,000 appear small. One should, however, not forget that these figures are averaged in time and space and therefore hide the real problem, e.g. droughts and floods. One can still use the ratio alpha of withdrawals and available renewable resources as an indicator. Due to the variability of the quantities involved, it is the experience that a value of alpha > 0.4 already reflects severe scarcity. On a global scale we find alpha = 0.31. This indicates that scarcity on a global level is a reality today, with the and world already experiencing very severe scarcity problems.