Underground water gained by lowering the water table.  There seems to be several terms in common usage. <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Aquifer" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Aquifer</a><p>Basically, if the water table is dropping then people are pumping out water faster than its being replaced.  If you look into when that water was put there you quickly get into geologic timeframes.  Aquifer&#x27;s often do flow meaning that specific drop may only be decades old, but replenishment rates in many places are vastly smaller than extraction rates.<p>EX: Some places in China have seen 10+ feet drops in the water table <i>per year</i>.<p>PS: “Fossil water” or paleowater is a related idea.  Basically water that&#x27;s been undisturbed for long periods. <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Fossil_water" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Fossil_water</a>