What is the definition of a water cooler chiller? A water cooler chiller is a device used to cool or chill drinking water. It is a compact unit that can be placed in any room of the house or office and connected to a water supply to provide a supply of chilled water for drinking. The chiller works by cooling the water in the tank via a compressor, and then circulating it through a cooling coil which keeps the water at a set temperature. The temperature is adjustable and the water can be kept at any temperature from chilled to cold or even hot. The chiller can be used to provide chilled water for drinking or to supply a chilled water supply to a variety of applications such as cooling of machinery or even fish tanks. The water chiller is an efficient and convenient way to ensure that your drinking water is always cool and ready to drink.