Abstract: A prefabricated water supply system for supplying water from an underground source to mobile homes or stock tank waterers and the like includes a riser pipe encased within an outer pipe spaced from the riser pipe. A third hollow pipe is located adjacent to the riser pipe and parallel to it. The space between the outer pipe and the riser pipe and third hollow pipe is filled with a rigid polyurethane foam insulation. A heat tape controlled by a thermostatic switch is located within the third pipe and a pair of end caps are used to hold the unit together. The provision of the third hollow pipe for the heat tape permits ready insertion and removal of the heat tape even after the unit has been installed in the ground under a mobile home or a stock tank waterer. An access opening aligned with the upper end of the third pipe is provided in the top end cap for facilitating this replacement and removal.