Abstract: A heat pump system can be reversed to either heat or cool a controlled space, such as environment in a building. In a typical use, such as heat pump system extracts heat or cold energy from the surrounding air around the building. A water-to-refrigerant heat exchanger is added to the refrigerant loop of the heat pump system along with a control system to operate water flow and a thermal energy exchange process. Addition of the water heat exchanger can add the heat or cold energy stored in a pool, or other external water reservoir, into the heat or cold exchanging process. Depending upon surrounding conditions, the automatic control system can switch in-between the energy sources, or use a combination of them, to improve efficiency the heat pump system.