Global freshwater resources and fluxes are poorly quantified and large differences exist between various published estimates. This is particularly pronounced for continental groundwater, which is estimated to make up between 0.3-1.6% of the global water budget. Only a fraction of this groundwater is useable, however, due to high salinity of mostly deeper groundwater. In addition, most subsurface processes are slow and memorize impacts over generations, so that only far-sighted groundwater use and protection is sustainable. Higher expected future water demands for irrigation, industrial, and household purposes require more investment in freshwater characterization and quantification. Factors including climate change, large-scale reservoirs, re-channeling of streams, expansion of urban centers as well as chemical and microbial loading need to be taken into account. Promising methods to reduce pressures on freshwater include prevention of chemical and biological input, desalination, artifi cial groundwater recharge, and economic use of water, such as drip irrigation.

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