Indigenously developed polysulfone Ultrafiltration (UF) membranebased domestic and industrial water purification units were evaluated for their ability to filter bacteria and viruses from water. Escherichia coli (10 5 cfu/ml) and P1 phage (10 6 pfu/ml) were filtered through a Domestic Water Purifier (DWP) (dead-end UF unit) and a large-scale spiral water purifier (cross-flow UF unit) and the filtrates were analysed for bacterial and phage counts. Both units were found to be efficient in the complete removal of E. coli and a 99.99% removal of the P1 phage was observed. Both the domestic and industrial water purifiers are highly efficient in the removal of bacteria and viruses. UF membranes were also characterised for Molecular Weight Cut-Off (MWCO) by the polyethylene glycol and polyethylene oxide methods, which showed that MWCO was 60-65 kDa. These MWCO results were further validated using the Bovine Serum Albumin (BSA) rejection behaviour of these membranes, which showed about 90% rejection. The technique involving the estimation of MWCO, coupled with the rejection characteristics of E. coli and P1 phage, provides an excellent tool to evaluate the efficiency of water purifiers based on UF membrane technology. Copyright © 2009 Inderscience Enterprises Ltd.