a water / steam system for a combined cycle power plant and related method for operating said system are provided . the system comprises a heat recovery steam generator providing a flue gas stream path for extracting heat from a flue gas stream exhausted from a gas turbine , the heat recovery steam generator having a low pressure section including a low pressure evaporator arranged along the flue gas stream path for generating low pressure steam at a low pressure input level for a main input of a low pressure steam turbine . to use heat a low temperatures , embodiments of the system provide that in the low pressure section , additional sub low pressure steam , at a sub low pressure level below the low pressure level , is generated by a sub low pressure evaporator in the flue gas stream path .