Biological filtration on biological activated carbon (BAC) used for the treatment of potable water is very effective in removing biodegradable dissolved organic carbon (BDOC). This type of filtration can also be used to simultaneously remove ammonia. When nitrification is properly optimized in biological filters, the risk for both nitrification and the presence of nitrate in the distribution system is greatly reduced. The three main objectives of this study were to: identify factors that influence nitrification in BAC filters during the treatment of potable water; explore the kinetics of the two nitrification steps (the nitrosation of nitrites to nitrates and the nitration of nitrites to nitrates); and, rank the factors controlling the effectiveness of nitrification in BAC filters based on the results of pilot studies.