Transport models in reverse osmosis (RO) desalination have been extensively studied taking into account various factors such as temperature, fouling, etc. However, there are not many models that describe the behavior of a desalination plant over long time periods. These models depend on operating time and empirical parameters to estimate the flux or the average water permeability coefficient (A) decline. The proposed model separates the decline of A in two stages, the first stage refers to a more pronounced decline due to initial compaction and irreversible fouling and the second stage describes a more stable period with less slope. The model is based on the superposition of two exponential functions, which depends on operating time, empirical parameters and fouling potential of the feedwater (k(fp)). Ten years operating data of a brackish water reverse osmosis (BWRO) desalination plant were used. The obtained results with the proposed model showed a slightly better fit than previous models, but giving meaning to two different behaviors separated in two stages. (C) 2016 Elsevier B.V. All rights reserved.