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Understanding the removal of organic constituents is essential for the production of safe drinking water.  Dissolved organic matter (DOM) removal is needed to mitigate disinfection byproduct (DBP) formation and inhibit microbial regrowth in the distribution system. Slow sand filters (SSF), although globally widely used, are no longer used in the U.S. due to their larger footprint; however, rapid media filters (RMF) have a smaller footprint and are required for surface water treatment in the U.S. These RMF can be designed and operated as biofilters. Empty bed contact times (EBCTs) of biofilters vary from hours (SSF) to minutes (RMF), yet a knowledge gap exists between their DOM removal rates. The goal of this work is to evaluate the removal of DOM by extended biological RMF. Preliminary work, at bench scale, evaluated biofiltration efficacy on twenty-seven influent Colorado waters. Total organic carbon (TOC) removal of coagulated water was evaluated at four different biofilter EBCTs (3.5, 7.5, 20, and 30 min). The easily biodegradable DOM was removed in the first 7.5 min., and additional removal of the slowly biodegradable DOM occurred in the 30 min. EBCT. An average of 5-13% TOC removal was seen in the 7.5 min. EBCT, and an additional 7-12% TOC removal was achieved at the 30 min. EBCT. Current work, at pilot scale, is applying biological treatment to source waters to increase DOM removal by extending the EBCT. Overall the information obtained from this work provides useful insight to water utilities planning to implement biofilters in their treatment train.