Diarrhoea and water-borne diseases are leading causes of mortality in developing countries. To understand the socio-cultural factors impacting on water safety, we documented knowledge, attitudes and practices of water handling and usage, sanitation and defecation in rural Tamilnadu, India, using questionnaires and focus group discussions, in a village divided into an upper caste Main village and a lower caste Harijan colony. Our survey showed that all households stored drinking water in wide-mouthed containers. The quantity of water supplied was less in the Harijan colony, than in the Main village (P<0.001). Residents did not associate unsafe water with diarrhoea, attributing it to 'heat', spicy food, ingesting hair, mud or mosquitoes. Among 97 households interviewed, 30 (30.9%) had toilets but only 25 (83.3%) used them. Seventy-two (74.2%) of respondents defecated in fields, and there was no stigma associated with this traditional practice. Hand washing with soap after defecation and before meals was common only in children under 15 years (86.4%). After adjusting for other factors, perception of quantity of water received (P<0.001), stated causation of diarrhoea (P=0.02) and low socio-economic status (P<0.001) were significantly different between the Main village and the Harijan colony. Traditional practices may pose a significant challenge to programmes aimed at toilet usage and better sanitation.