Groundwater reserves which will, in the foreseeable future, either run out or become increasingly difficult to access
Unsustainable irrigation water
"Using a global hydrological model and statistics on land use and economic development, we have determined how much more groundwater is used for irrigation than is naturally supplemented by rainfall. This groundwater use is not sustainable.
Depletion of groundwater supplies
Our research shows that, worldwide, about 20% of irrigation water is extracted from groundwater in a non-sustainable manner. Moreover, the amount of groundwater extracted by such non-sustainable means has tripled since 1960. This has led to a depletion of groundwater supplies in many areas in the world. Today, more and more food is being produced with water that will, in the foreseeable future, either run out or become increasingly difficult to access. ,Moreover, the fact that a growing world population is partly dependent on non-sustainable water sources, will eventually lead to food shortages"
Marc Bierkens, Professor of Hydrology