Heat pump is how air conditioners work, a heat pump that heats works in reverse. There's no drilling needed, that would be geothermal.

Heat pump water heaters do save about half the cost in electricity over a conventional resistive-only water heater, and are optimal for places with basements, as they also dehumidify; or in warm climates, as they cool the air. So it's also useful for long term perishable storage like a root cellar would be, or in a laundry room. They do cost 3x as much, though.

Residential heat pumps for heating and cooling in the US is relatively new, and I've had nothing but problems with mine - so much so that I just received a full refund on the purchase price of my unit because of manufacturing "defects".