The reason the water is colder is because it is traveling underground most of the time where the temperature is generally a constant 55 degrees F. Direct Exchange geothermal energy systems use this to provide both heating and cooling, but instead of tap water they generally use refrigerant in a closed loop system. When that refrigerant has given up its heat (or gained heat if used in cooling), it is sent back into the earth where it is warmed or cooled to 55 degrees.