As the quality of raw water deteriorates, a number of additional treatment techniques have been developed and adapted to water treatment for producing a safe and aesthetically satisfactory drinking water. One of the various alternatives is to use a biological process, such as a submerged bed filter, as the first process in the treatment train followed by conventional treatment processes. Biofilm process for the pretreatment of water is suitable for advanced treatment as the biofilm can keep microorganism, at low organic concentrations. This article examines the application of biological treatment strategies to tackle the current problems of the water industry. Pilot-scale biofilm reactors were evaluated with various contaminants frequently encountered in water supplies. The studies focused on the production of biologically stable water, increased disinfectant stability, and reduced formation of disinfection by-products. Results showed that the finished water became more biologically stable even though the reduction of organics was relatively low. Biofilm grown on natural water supplies was effective in removing THMP (trihalomethane precursor) as well as taste and odour compounds, such as geosmin. (C) 1997 IAWQ. Published by Elsevier Science Ltd.