The biofouling potential in industrial water systems consists of microbial biofilms and nutrients which can be considered as potential biomass. The basic mechanism of biofilm development involves the conversion of dissolved nutrients into locally accumulated biomass. Biofouling occurs only when the extent of biofilm growth meets a threshold of interference. It is not necessary to kill all biofilms, it is possible to live with biofilms as long as this operational defined threshold of interference is not exceeded. The concept presented involves a biofilter upstream of a system to be protected. As biofilm growth is limited by the amt. of nutrients available, the growth of biofilms in the biofilter will occur at the expense of the nutrients detd. as biodegradable dissolved org. C. Thus, downstream of the reactor the nutrient concn. is reduced and less biofilm develops in systems. This concept has been investigated in an heat exchanger plant system with RO-systems and proved to be feasible.