The present invention relates to a water supply apparatus installed in a cattle shed for raising livestock such as milk cows or the like. More particularly, a drinking trough including an inner casing, an outer casing and an elevating body is installed below an upper surface of a water tank, and the elevating body has a bottom with an open/shut valve body. A water supply pipe with an on/off valve, a water drain pipe, an overflowing water pipe, a heater, a water level sensor and a temperature sensor are installed in the water tank to enable livestock such as milk cows or the like to drink from the elevating body containing a predetermined quantity of water. The open/shut valve body installed on the elevating body enables a constant quantity of water to be contained in the elevating body, and simultaneously prevents foreign substances from entering the water tank to prevent the water from being spoiled. In addition, the drinking trough arranged in the upper portion of the water tank is opened to a minimum degree for enabling the drinking of water, and thus causes a minimum loss of heat, thereby achieving improved heat-insulating effects in the wintertime, and providing clean water with an optimum temperature at all times.
