With underground energy [i.e. ground water (well water, water in underground pipe or other form of surface water)] as main energy and with electric energy as auxiliary energy, the water/ground source heat pump water-to-water screw unit exploits and utilizes inexhaustible but difficult-to-use, low-grade renewable energy resources from underground through advanced equipment to change them to high-grade energy sources. Thanks to use of underground energy, the unit can operate stably without being affected by outdoor environment and climate and is immune to the problems such as defrosting and community heat island effect that may occur on air-cooled heat pump units.