The invention relates to a method for operating a recirculating waste heat steam generator (1), in which in a pressure stage of the recirculating waste heat steam generator (1) the feed water mass flow is guided on the basis of a specified desired value in order to control the water level in a drum (8). Said method should give a recirculating waste heat steam generator a particularly high degree of efficiency and simultaneously a particularly high level of operational flexibility. For this purpose the thermal input introduced into an evaporator (12) of the pressure stage is used as input variable in the determination of the desired value.