Desalination of brackish water containing silica at high recovery levels leads to a rapid flux decline, due to the precipitation of a colloidal solution consisting of polymerized silica nano-particles. The critical flux (CF) phenomenon postulates that there is a certain permeate flux level below which the rate of flux decrease due to membrane fouling becomes negligible. The aim of this paper was to develop a simple technique for detecting the existence of a critical flux threshold limit under conditions at which the membrane surface is exposed to a constant precipitation potential. A series of experiments was carried out in a silica scaling tubular RO system. Experimental conditions were controlled such that the dissolved silica content on the membrane was held at the same supersaturation ratio level of 2.1-2.2 The rate of flux decline was found while varying the initial permeation flux value over the range of 17-45 l/h m(2) to remain constant, irrespective of the permeate flux level examined.