Abstract: An animal watering unit includes a cylindrical tank which is closed at the bottom and buried on end with its open top near ground level. Water is supplied to the tank through supply piping controlled by a float operated valve. An insulated disk serves as a cover for the tank to inhibit heat loss through the top and also as a float which controls the float valve through an adjustable chain linkage. Incoming water is discharged into the tank in a swirling pattern at the bottom. An insulated collar surrounds the upper portion of the tank near the ground surface. This construction takes advantage of the subsurface ground heat to maintain the water temperature above freezing without the need for an electric heater or other type of heater.