If you had a tunneling machine and wanted to tunnel towards fresh water underground, how would you find the water? I'm imagining some sort of sonar, but would you need triangulation of some kind? Assume a runaway greenhouse effect and surface temperatures of around 500f, so no surface water.

  • $\begingroup$ possibly maps? think about it if there's a river at point a which goes underground at point b which makes a line to point c. Dig near point c. $\endgroup$
    – Topcode
    Apr 4 '20 at 22:05
  • $\begingroup$ I've been omitting too many details, sorry. Assume no surface water. $\endgroup$
    – Josiah
    Apr 4 '20 at 22:10
  • $\begingroup$ I don't believe subterranean water will last forever given surface temperatures of 500f. Over geologic timescales, the whole planet will be heated through. So unless this hellish climate is a new development, there won't be any water for you to find even with the right gear. $\endgroup$
    – Ryan_L
    Apr 4 '20 at 23:45
  • 2
    $\begingroup$ As we used to say in hydrology class: "Well, well, well." $\endgroup$
    – user535733
    Apr 5 '20 at 0:01

Just dig. Almost anything deep enough underground floods, you need constant pumping to keep it clear.

If in doubt you could always use existing cave networks which are known to be flooded as a starting point.

  • $\begingroup$ I wonder whether that's still true when there is no liquid surface water. The water in today's caves comes directly from the surface or from aquifers that are fed from the surface, doesn't it? You'd need condensation of some kind. Perhaps deep down it's below boiling, so the moist air from the surface would condense. Dunno. $\endgroup$ Apr 30 '21 at 7:31

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