Combined storage tanks 2-in-1 for heat pump systems to be used for hygienic domestic water heating in through-flow principle and for heating water or for water cooling. The storage tank serves 2 functions. Fresh-water heating takes place in the upper part of the tank, the lower part buffers the heating return and provides defrost energy for the heat pump. The insulated structure of both tank areas permits large temperature differences. Thus, simultaneous heating up of the hot water and cooling operation of the surface heating system is possible through the heat pump in the summer. Separate heating elements can be retrofit for both storage tank areas.