Reverse osmosis (RO) has emerged as an alternative treatment in industrial water production. However, RO systems need suitable pretreatment to avoid membranes fouling. A demonstration study was conducted to assess improvements to RO pretreatment in the water treatment plant of a steel factory. Various pretreatment options, resulting from the combination of the existing treatment with different filtration stages, were tested. The silt density index (SDI) and the modified fouling index (MFI) were used to evaluate the performance of the different configurations. Throughout the experimentation period, it was not possible to assess the SDI of the filtration inlet water due to the high colloidal fouling, while the inlet MFI ranged from 9 to 458. Results showed that the dual-stage in-series filtration, including two pressurized filters, provided the best results, achieving SDI values lower than 5 and effluent MFI values lower than 1 under optimized operating conditions. Considering the fact that the MFI is a more accurate measurement as it takes into account the cake filtration mechanism, we conclude this configuration was able to provide enhanced RO pretreatment with a higher quality than the minimum required, despite the SDI not being lower than 3 with a reliability of 90%. (C) 2011 Elsevier B.V. All rights reserved.