Wells are totally fine, just to get that out of the way.
Strictly enlarging existing infinite/permanent water type terrain would be ok, keeping in mind it would have to proceed from the river/lake/pond outward. That’s a good hack on the concept 
Anything dealing with a non-infinite or non-permanent water supply necessarally requires water flow simulation, since if you have two connected water-filled tiles and one goes empty, it’s nonsensical for the next one over to stay full. The way our map infrastructure is coded, it’d be a HUGE PITA to try and keep water flow consistent. DF handles this by having the map always loaded, I assume there is no water flow mechanic happenining in adventure mode, as it would run into the same problems.
If your goal is an indefinitely sustainable base and basic terraforming in support of that, you’re at the minimum pushing at the boundary of the game. The game is very strongly centered around a lone survivor, you know, surviving.
While we want to do NPC settlement like stuff, and probably running water and electricity in those areas, that will be a faction thing. I’m not planning on managing every litre of running water and every watt of electricity, which is what would be required to have a player managed large scale settlement.
At a small scale, like within a single building, water/electricity/heating/cooling sure, player controlled and fully managed resources, but like I said, player-controlled city-building is out of the scope of the game.
I’m not saying this will never change, this is a very organic and community-driven project, and if we have a good coder come along that wants to do all the heavy lifting for this kind of thing, I would almost certainly let it develop in that direction, but if I’m doing any of the heavy lifting, I just don’t think it’s a good fit.
