Abstract: A control system for a pump submersible in a well having a water pipe extending upwardly to a water source includes an isolation element that has one fluid chamber in communication with the water pipe and another chamber separated from the first by a flexible diaphragm. The second fluid chamber is filled with a non-toxic antifreeze control fluid and communicates with a fluid conduit which extends upwardly to a pressure switch. The pressure switch is mounted above-ground and monitors the pressure of the control fluid to activate and deactivate the pump. Since the diaphragm is flexible, the pressure of the control fluid corresponds to the water pressure in the water pipe. The isolation element is positioned in the well below the frost line so that all control parts in contact with water are located below the frost line, and all control parts located above the frost line contact only the antifreeze solution.