I am working on a some sub terrain dungeon material. Looking into caves and other such things, it occurs to me.
Does Athas have underground aquifers? I am not aware of anything in the canon which expressly says “no.” It is established that Athas does have functional wells and fountains. That plus oasis and mudflats would indicate to me that yes water does exist and gravity affects it as expected. So it would make logical sense for underwater aquifers.
The counter argument is that nothing in the lore that expressly says they do. Also, people can say there is too little water for even that. Certainly, there would be cave systems and the like carved out by water, that has long since disappeared. Some will argue that even this much water, in an aquifer, goes against the mood and survival elements of Dark Sun.
I see the following uses for such a thing in Dark Sun. This is just a start though.
Narratively speaking, these would be able to fulfill the role of oasis under the ground. Almost anything you could do with a oasis, you could do with an aquifer. I would say, it wouldn’t make sense for a trading route, though.
I see Water clerics, druids and to a lesser extent, Earth clerics going nuts over this. Some might even be willing to live entire lives underground to be near such a source.
If surrounding caves are dry, this would be a monster hotspot and/or guarded by whatever intelligent creatures are nearby.
Remember, it doesn’t need to be drinkable. It can be polluted, briny or something else.