Abstract: A method and apparatus for polishing a condensate is provided wherein the condensate contains both suspended and colloidally dispersed solid impurities, and also intermittent and variable levels of ionic impurities and dissolved silica. When the ionic impurities exceed a preselected level, a finely divided ion exchange resin mixture is first admixed with the condensate at a rate sufficient to reduce the level of such impurities to a preselected level within a preselected contact time period. Thereafter, the resulting condensate is passed through a membrane filtration device to remove such suspended and dispersed solid impurities. A simple, effective and reliable retrofittable apparatus adapted for use with BWR's fitted with precoat filter systems is provided.