A method, apparatus, and system and operation of surface equipment to generate steam while reducing the quantity of boiler blowdown and thereby increasing the amount of feedwater that is re-used or re-cycled in generating said steam. The present invention teaches that, on a sustained basis, the blowdown stream at the outlet of a once-through steam generator can be routed to the inlet of a second once-through steam generator that is in series with the first, that blowdown stream can be used to generate additional steam in the second once-through steam generator and further reduce the amount of blowdown, and that this can be accomplished without need of any treatment that reduces hardness or silica levels of the blowdown stream prior to its entering or during its entry into the inlet of the second once-through steam generator. The output of this second steam generator is a substantially dry saturated steam vapor stream and, complementarily, a blowdown stream whose mass rate has been reduced substantially from that of the blowdown stream exiting the first steam generator.