Many homes have heat pumps to heat and cool their homes. But aheat pump also can be used to heat water. Heat pump water heaters use electricity to move heat from one place to another instead of generating heat directly. Therefore, they can be much more energy efficient than conventional electric resistance water heaters. To move the heat, heat pumps work like a refrigerator in reverse.
Heat Pump Water Heaters work best in an unconditioned space like a garage but some can be installed indoors. There are some great financial incentives to replace your existing electric water heater with a Heat Pump Water Heater. More information at SmartWaterHeat.org, http://www.dsireusa.org/ and your local utility.