Older topics that may be related:
# # # #First, let's give inorganic materials a [SOLUBILITY] token. SOLUBILITY could go from 1 to 10, or follow some sort of real-world measurement (more likely). Still listening? Good!
Now we have volcanic regions already. Let's improve them. Since we don't have tectonics simulations (yet), we place hot pools and springs in mountains and near volcanoes. This will tie back into SOLUBILITY: pools are most likely to form over more soluble rock types and in aquiferous regions. Throughout the year, they maintain a temperature of over 40 degrees centigrade (10072 Urist) and will cause scalding if anything lingers in them for too long. However, these hot spots are zone-based, not water-based, so draining a hot spring (good luck, they're quite deep) will leave a hot, muddy crater and some cold water nearby. They will slowly refill as water gushes up from underneath. But how do they look underneath?
These are different than murky pools - they're heated by magma, so they go down deep. Very deep. These pools can be over fifty z-levels deep, and they should always reach near the magma layer - they will generate like our current volcanoes, except they're separated from the magma by a few layers of obsidian, and the tube around them isn't obsidian but the normal rock surrounding them. Geysers would be nice, but not until temperature is more sophisticated and computers are too (PHWOOSH, wow, lag!!).
Civilizations like hot springs. Elves may be able to treat them as shrines if they're in the sacred forest, goblins could toss mutilated sacrifices into the depths, humans could actually bathe in them and build bathhouses and dwarves would build bathhouses too, although they would probably also treat the hot springs as being holy and toss relics into the pool. An enterprising player who drains the springs could recover ancient artifacts and treasures.
Now, adventurers will love these things, because they don't freeze. Unfortunately, springs over soluble rock (which are more common, remember) are likely to be laced with that rock, making the water less filling or even too smelly/rocky/cloudy/dirty to eat (water laced with brimstone, yum yum). The rare springs over less soluble rock-types will be fine.
Civilizations could want spring water if you've got it - maybe your water laced with pitchblende is just the ticket to better health (don't try this at home!). "Spring water" would be a valuable trade good, and you could make a task at the Still (I can't think of anything better) to collect spring water in a vial or flask.