Abstract: An automatic water fountain has developed for supplying warm-fresh water to a livestock barn to raise the livestock, such as milk cattle. A water supply unit is consisted of an inner case, outer case, floating case installed inward of top portion of the water tank, a check valve installed to the bottom of the floating case, drain pipe, overflow pipe, heater, water level sensor and temperature sensor. The water supply pipes with level limit valve are connected to the water tank. The container of floating case is filled with warm-fresh water, so that the livestock drinks the water, freely. The check valve of the floating case is automatically operated to maintain the constant water level all the times and filter offs the foreign objects into the water tank for preventing to contaminate the water. The container has minimum opening area to drink for minimizing the heat-loss. Therefore, it will effectively provide the warm-fresh water for livestock all the time, especially for the winter time.