40 or 50 ft is the minimum in my area in mid michigan. we had a 30ft well with a static level of 20. hard water, iron bacteria, sand. etc. we eventually bit the bullet and had a new deep well drilled at a depth of like 200 or 300ft, i can't remember. they called it a rock well. water was very clear, very clean. before installing this new well, we had a softener and an iron filter, and two of those paper and carbon pre filters installed before this stuff and the water was still nasty. make sure to have your water tested for coliform, nitrates, iron bacteria, lead, arsenic, etc. I think these are all mandated, but if not make sure. they may have to chlorinate the well to clean it up, too. we did that fairly often. we had to pour bleach down the well, let it sit, then run it all night. the water still smelled the next few days and i made sure not to drink it. this is just my opinion, as a homeowner. i am not a plumber or water quality expert.