A heat pump water heater 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 another natural water source, it may be an option worth considering.
All types of heat pumps can provide excellent year-round home temperature control by pumping heat in during the winter months and removing it during the summer. The main difference between the types of heat pumps is where they get the heat or dispose of it.
Traditional air source heat pumps get their heat from the air outside, as even relatively cold air actually contains a substantial amount of heat. They use this heat to keep your house warm in the winter, but as the outside temperatures go down below freezing, these heat pumps can become less and less effective.
Water source heat pumps, on the other hand, work on basically the same principle as air source heat pumps, but they extract heat from a body of water rather than the air. They do this by cycling water through a system of pipes that are laid out at the bottom of a body of water. As the water cycles through, it gathers heat from the lake or reservoir and then carries it back to your house.
In the summer, the process is reversed and heat is carried out of your house and expelled in the cooler water outside. As air source heat pumps, water source heat pumps are slightly more efficient at cooling rather than heating, as even deep water will eventually get cold during the winter months. However, the water is still often warmer than the air, and so water source heat pumps can be a good alternative if you live in a slightly cooler climate.
Of course, you do also need to have access to an appropriate body of water to have a water source heat pump installed, which makes it something that is not available to everyone. But if you do live near such a body of water, a water source heat pump is definitely something worth considering.