Water storage : health risks at different scales

Water is stored to facilitate access, and at all scales from huge reservoirs to small pots within the household. But there are health hazards as well as benefits from water storage; these are explored here within the frameworks of geometry, process and functional classification of risk. Hazards depend upon ease of access of people and other biota and pathogens to the water. Insect vectors of disease may breed in the water. Risk tends to decrease in larger water bodies. Methods to reduce the health hazards of large dams are well studied, even if often ignored, but those for small dams are less clear, requiring a choice appropriate to the locally relevant pathogens, and further research attention. Measures against specific diseases will depend on the preexisting levels of endemicity, and on how far alternative methods of treatment and prevention are available. [authors abstract]