Diarrhoeal disease: current concepts and future challenges. Water, sanitation and diarrhoea: the limits of understanding.

This paper reviews the application of epidemiological understanding of diarrhoeal disease to interventions in water and sanitation. Over the past 20 years, great efforts have been made to elucidate the relationships between water supply, sanitation and diarrhoeal disease. At the outset, it was hoped that improved understanding of these relations could provide a rational framework for the planning of public health engineering interventions. This paper also reviews historical and recent perceptions of water, sanitation, and diarrhoeal disease, and summarizes progress to date. On the one hand, some fundamental ideas about the relative importance of water quality and quantity in the transmission of diarrhoeal disease have changed, and there is increased recognition of the complex interrelationships between interventions, hygiene behaviour and health. On the other hand, our understanding of the impact of interventions is painfully incomplete, and is unlikely to improve dramatically in the near future. While further research can usefully illustrate a variety of interactions in specific contexts, globally applicable planning guidelines and design criteria appear a dangerous will-o'-the-wisp. While we know more than ever before about water, sanitation and diarrhoea, much remains unknown, and is perhaps unknowable.