Water table
Chart of water table of Velara III
A water table is a geological layer on a planet. Comprised of water called ground water, this layer was a key precondition to supporting life on Class M world. The ability to access and exploit the water table was a key part of the Federation's terraforming process.
In 2256, after a drilling accident on the Crepusculan homeworld, the ambient radiation from this event dried up the water table, threatening the Crepusculans with extinction. (DIS: "The Vulcan Hello")
The water table on Velara III existed as a very thin ribbon between the sandy surface soil and harder rock layers below. (TNG: "Home Soil")
In 2366, Rana IV's water table was tainted, necessitating the removal of Kevin Uxbridge and Rishon Uxbridge from the planet. (TNG: "The Survivors")
Later that year, Beta Agni II's water table was sabotaged with tricyanate by Kivas Fajo as part of a plot to kidnap Lieutenant Commander Data. (TNG: "The Most Toys")