A substantial component of BRAC's WASH programme involves educating rural Bangladeshis about safe water management, good hygiene and the causes of diarrhoea. By conducting questionnaires and focus group discussions in two BRAC WASH villages and one control village, this investigation sought to assess the impact of BRAC's programme on knowledge, practices and diarrhoeal burden, to explore the extent to which knowledge determines practices, and to evaluate which factors were most predictive of diarrhoeal incidence. It was found that the programme had a beneficial effect on the subjects' knowledge and practices, and on the diarrhoeal incidence among their children. Furthermore, except for where personal financial expenditure was required, practices tended to follow on from knowledge. However, BRAC's intervention affected neither the frequency of soap use in handwashing by the mother, nor the child's consumption of unclean water outside of the home. These factors, along with the child's consumption of unclean water inside the home, were shown to be those most predictive of diarrhoeal incidence among the under-fives. It is recommended that BRAC continues to emphasize the importance of these points, while also potentially promoting the use of less costly alternatives to soap and cheaper point-of-use treatment materials, to induce positive behaviour change.