As illustrated in the animated schematic below, two units in operation with Unit “A” in cooling mode while Unit “B” is in heating mode.
A water source heat pump operates much like a traditional air source heat pump except that it extracts and dissipates heat by way of water instead of air. This is certainly not a type of home comfort system that will be available to anyone, but if you live in an area close to a well, lake or other natural water source, it may be an option worth considering.