After finding ground water, all tiles I've tried to build on give "you can't build on that on this type of terrain" message. I've tried paved, plowed, dirt and forest. The same type of tiles that don't have water give the proper "the water runs to deep here" error.
You said everything but surveying the ground and making it flat, are you doing that? *edit* It seems that well area cannot be accessed because the water is "too deep". Find another.
I'm not trying to build on tiles that give an error about the water being too deep. I'm trying to build on water that I doused, but instead get "you cannot build on that type of terrain" errors no matter what terrain I put down.
It seems the tile under the handle of the well also needs to be valid. The interaction is a little strange since an empty forest tile next to the handle wasn't valid, but turning the handle to face my brickwall with stone underneath made it able to be built.
"The psychological trials of dwellers in the last times will be equal to the physical trials of the martyrs. In order to face these trials we must be living in a different world."