Abstract: The present invention discloses a water heater/cooler having a water tank with a wall formed from material having heat transfer properties. A tube which carries a refrigerant fluid is applied externally about the tank wall. A heat-conductive material is coextensive with the length of the tube to allow the tube to be in heat-conductive contact with the tank wall. At least one layer of material is tightly wrapped about the tank wall and the tube.