Copolymer of acrylamide with N-benzyl-4-vinylpyridinium chloride (PAAM-co-BVP) produced coagulation and sedimentation of Escherichia coli, Bacillus subtillus, Pseudomonas aeruginosa, and Staphylococcus aureus. Addition of more than 50 mg L-1 of PAAM-co-BVP produced bacterial flocks that precipitated at a rate of around 200 cm h(-1). Supernatant population reduced in the range 1/30,000-1/25,000,000. Reduction of supernatant population was most effective when about 200 mg L-1 of PAAM-co-BVP was added. PAAM-co-BVP was highly biodegradable and the half-life estimated was 2.4 days when treated with activated sludge. The ratio of biochemical oxygen demand for 5 days (BOD5) to total organic carbon (TOC) was 0.607. Coagulation and sedimentation of bacteria using PAAM-co-BVP is expected to improve the water disinfection processes by saving chlorine and other hazardous chemical fungicides and by reducing the formation of trihalomethanes and other toxic chemical materials. (c) 2006 Wiley Periodicals, Inc.