My latest attempt at a fortress took place oceanside, in 7 layers of black sand, between sedimentary stone, obsidian and many many aquifers.
All went well, safe for that last bit. Aquifers. I havnt had so much trouble with those due to my tendency to settle in mountains, but with this fort I had to make my main mining shaft through several layers of aquifer.
Through some dwarven science, I found out that aquifers still produce water when all orthogonally open tiles are walled off, that I can mine through aquifers when there is another aquifer below, and that my dwarf powered magma pump failed to push magma upwards (dispite having no diagonal channels).
So thinking I had enough to get through the first layer of watery sand I did some channeling, walled of a smaller bit of aquifer, and took to applying magma on the aquifer below that one. All went well, untill I removed the temporary walls that contained the mostly evaporated magma.
Not only did I have a flaming miner setting my barracks on fire (didnt mind that, it was kind of funny), there was also water being produced out of nowhere.
That water wasnt spawning while the magma and the walls were still there, or even before I pumped in the magma. Only after I finished forbidding my former miners oh so aluring !!socks!! and looked back everything was all flooded.
So what went wrong? Whats making that spot surrounded by constructions spawn water?