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Background: People in rural Bangladesh have a poor understanding of the link between use of contaminated surface water and disease. An inexpensive point-of-use water treatment agent was developed to purify surface water., Methods: Surface water was collected from various sources in Bangladesh from February 2007 to January 2008. Microbiological and physicochemical parameters of raw and treated surface water were analysed. Water was treated with a mixture of alum potash, bleaching powder and lime, or with each agent individually., Results: Raw water was contaminated with bacteria, the counts for total coliforms, faecal coliforms and faecal streptococci being 26,431, 14,548 and 240 colony-forming units (cfu) 100 ml(-1), respectively. These counts fell to 0 cfu 100 ml(-1) after treatment with the mixture. The count of artificially introduced Vibrio cholerae was also reduced to 0 cfu 100 ml(-1) after treatment. Treatment of raw water altered the pH from 6.90 to 6.87, turbidity from 21.61 to 3.55 nephelometric turbidity units (NTU), residual chlorine from 0 to 0.09 mg litre(-1), conductivity from 124.03 to 229.96 µS cm(-1), and total dissolved solids from 59.40 to 199.25 mg litre(-1). All these results of treatment were within the range recommended by the WHO as acceptable for drinking water., Conclusion: The mixture of alum potash, bleaching powder and lime described can be safely used to disinfect contaminated surface water to make it suitable for drinking and other household purposes in Bangladesh.