Fossil water

UNESCO defines fossil groundwater as "water that infiltrated usually millennia ago and often under climatic conditions different from the present, and that has been stored underground since that time.

Determining "fossil" status—whether or not that particular water has occupied that particular space since the distant past—involves modeling the flow, recharge, and losses of aquifers, which can involve significant uncertainty.

Fossil water is extracted from these aquifers for many human purposes, notably, agriculture, industry, and consumption.

[4] Aquifers are typically composed of semi-porous rock or unconsolidated material whose pore space has been filled with water.

More commonly, fossil water is found in arid or semi-arid regions where the climate was significantly more humid in recent geologic history.

[10]The Nubian Sandstone Aquifer System is located in northeastern Africa, under the nations of Sudan, Libya, Egypt, and Chad, covering about 2,000,000 km2.

In modern times, as demand increases, avoiding rapid depletion and international conflict will depend on careful cross-boundary monitoring and planning.

Libya and Egypt are currently planning development projects to withdraw significant amounts of the aquifer's fossil water for use.

[12] In the northern region of the Kalahari, a deep aquifer in Cave sandstone was found to have isotopic signatures that suggested it had been confined with little to no leakage for long periods of time.