Fossil water

The term fossil water refers to water that has been locked up, so it is not part of the "water cycle". Deposits of fossil water, unlike normal ground water, is a non-renewable resource.

Glaciers laid down during the last ice age is a form of fossil water.

There are reservoirs of fossil water deep under porous arid regions, last recharged there prior to a change in climate. The very dry Sahara desert has a long cycle, tied to the ice ages, where it does receive rain, and is green, that is tens of thousands of of years long, and there is a vast reservoir of fresh water buried under the desert.

The Yangtse River, Mekong River, Bramaputra River, and several other large rivers, all have their headwaters under large glaciers in the centre of Asia near the Himalayas. A billion people rely on the meltwater from those glaciers.