I was thinking a deep pit would probably reach stone, so a pneumatic drill would be needed to dig farther for a well. A cistern would also be good. Really if the well hit an aquifer (generated in the map codes) it would be a rather large amount, but then it may be contaminated (AKA: sewers built through it or acid rain deposits). But if its not connected to an aquifer then the water would be fine, but in limited supply.
Also acid rain… If we assume the well has a roofing then the rock around it would filter it.
I just had a though, if you dug down into an aquifer with a drill. You would probably die, unless you had a good swimming skill. (Crafting should take a rope, pnumatic drill, 4 2x4’s, and a good construction skill.