I had been building this megaproject (obsidian-casting a tower that reaches from the clouds to the underground curious thingy) for 18 dwarf years now. Needless to say, this project requires a sizable infrastructure to support all the miners and masons on the site.
My watersource has been three wells that connect directly into the underground lake I have discovered on the first cavern. The reason I said 'has been' is that I discovered an annoying fact about the lake; it is finite. I found this out just recently when I sent out my militia and mason squad to block off one of the access stairwells to prevent a possible FB intrusion. The lake stops just two tiles short of the map edge. The entire water system is contained within the map, which, if my knowledge is correct, prevents the lake from refilling.
In every single fortress I have built to this day I relied upon extremely large supplies of water to power my automated goblin killing systems and other related uselfullless dwarven contraptions, and this lack of an infinite watersource is a very large setback. So, I'd like some advice on this. Is there a way to obtain a sustainable water supply without an easily reached infinite source? If not, what methods can I use to make sure I at least have drinking water? Expected population when my planned fort matures is around 180.
EDIT: My pumpstacks for obsidian casting operations have already depleted a portion of the lake. Also, additional explorer sorties into the caverns have revealed a second, larger lake on the second cavern, but sadly it also is finite...