A top-filling watering system configured to provide water to livestock, includes a water basin having an upstanding wall, and a reservoir securely mounted to the water basin. The reservoir includes a top wall integrally formed with a circumferential wall defining an open end connected to an interior cavity defined between the top wall and the circumferential wall. A filling opening is formed through the top wall. The filling opening is configured to allow water to be filled into the interior cavity. Another reservoir is capable of nesting within the interior cavity when the reservoir is not securely mounted to the water basin.
