The effect that biofiltration had on the fouling behaviour of several commercial nanofiltration (NF) membranes used for drinking water treatment was investigated using a bench-scale set-up. A dual-media anthracite-sand biofilter was used to pretreat a humic acid-laden solution spiked with a solution of pharmaceutically active compounds and for each membrane type, the performance using the effluent of the biofilter as feedwater was compared to membrane performance in the absence of pretreatment. Chemical, microbiological, and morphological analyses were carried out to evaluate the fouling performance of the membranes. A slight decrease in the organic carbon and the viable counts (measured as heterotrophic plate counts) deposited on the membrane was observed in all cases where biofiltration was used as pretreatment. The smallest organic fraction was able to get inside the pores of the looser NF membrane causing standard blocking. Biofiltration was able to considerably reduce the rate of flux decline to one third or less of that decline observed with the membranes that did not have pretreatment.