[en] The present paper describes the influence of the secondary side Water Chemistry on the operating behaviour of KWU U-tube steam generators. This description includes the operating experience both with AVT (All Volatile Treatment) and PO₄-treatment of the U-tube steam generators. Various aspects of design and tube material and their effect on operational experience regarding flow distribution, corrosion product behaviour and the corrosion resistance in aqueous media have also been discussed. It has been concluded that at present time on the basis of the proved design, material and chemistry of KWU U-tube steam generators there is no need for a change in any of the given parameters. (orig.)