I am trying to help a friend who is out of town for a few weeks. We are in southern Florida. His family is without water. I had pulled his pump, it sits at about 125'. The water table is currently at about 15' in the well. I found the pump had unscrewed. He had a set screw on the pump but it wasn't used. I called him and he said it has come off a few times over the years. He said he didn't use the set screw again because the last time when he pulled it the coupling was broken at the screw. I found that the down pipe is 1 1/4" schedule 40 pvc with a schedule 80 thread adapter at the well pump. The well pump has a nylon or plastic thread on it. There was no thread sealant tape. I added Teflon tape and screwed it back on. I pulled the set screw and predrilled the schedule 80 to try to avoid stress cracks. I the set the screw and put it back together. Three days later and its broke again. I believe I am going to find a similar situation. What would cause this darn thing to keep coming off? I am sure there is a better way to set this up. Torque arrestor?

The bladder tank for the well is good and all the house equipment/surface pump works fine, of course it needs water...

Thanks for your thoughts, Jerome