Disease acquired by drinking water contaminated at its source or in the distribution system, or by direct contact with environmental and recreational waters. Water-borne disease results from infection with pathogenic microorganisms or chemical poisoning.
These pathogenic microorganisms include viruses, bacteria, protozoans, and helminths. A number of microbial pathogens transmitted by the fecal-oral route are commonly acquired from water in developing countries where sanitation is poor. Viral pathogens transmitted via fecally contaminated water include hepatitis viruses A and E. Important bacterial pathogens transmitted via fecally contaminated water in the developing world are Vibrio cholerae, enterotoxigenic Escherichia coli, Shigella, and Salmonella enterica serotype Typhi. Water-borne protozoan pathogens in the developing world include Giardia lamblia and Entamoeba histolytica. The major water-borne helminthic infection is schistosomiasis; however, transmission is not fecal-oral. Another water-borne helmenthic infection is dracunculiasis (guinea worm infection).
In developed countries, fecal contamination of drinking water supplies is less likely. However, there have been outbreaks of diseases such as shigellosis and giardiasis associated with lapses in proper water treatment, such as cross-contamination of waste-water systems and potable water supplies. Animals are therefore more likely to play a role in water-borne disease in developed countries. Bacterial pathogens acquired from animal feces such as nontyphoid S. enterica, Campylobacter jejuni, and E. coli serotype O157:H7 have caused outbreaks of water-borne disease in developed countries where water is not properly chlorinated. Hikers frequently acquire G. lamblia infections from drinking untreated lake and stream water. Giardia lamblia may have animal reservoirs and can persist in the environment. A recently recognized pathogen apparently resistant to standard chlorination and filtration practices is the protozoan Cryptosporidium parvum. This organism is found in the feces of farm animals and may enter water supplies through agricultural runoff.
Chemical poisoning of drinking water supplies causes disease in both developing and developed countries. Lead, copper, and cadmium have been frequently involved. See Cholera, Escherichia, Medical parasitology