Microbial removal of nitrate from drinking water was studied in laboratory columns packed with unprocessed short fiber (low quality) cotton (Gossypium hirsutum). Cotton served as the sole chemical and physical substrate for the microbial population. Removal of nitrate was rapidly achieved without the formation of nitrite. Cotton (cellulose)-dependent denitrification was affected by changes in temperature: denitrification rates at 14°C were approximately half of the rates observed at 30°C. The cotton was entirely consumed in the process. In a fresh reactor, colonization of substrate by bacteria appears to be the rate limiting factor in the removal of nitrate.