28.1 Concept Check Drinking water quality is determined by counting coliform bacteria. Strict adherence to uniform microbiologic standards make this method a reliable and reproducible indicator of fecal contamination in all public water supplies in the United States. Filtration and chlorination of water supplies significantly decreases microbial load. Application of water purification methods to drinking water is the most important public health measure ever devised.
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28.2 Concept Check Wastewater treatment is primarily concerned with removing sewage and industrial wastes, thereby reducing the BOD (bio-chemical oxygen demand) to acceptable levels. Primary, secondary, and tertiary treatment of water involves physical, biological, and physicochemical methods, respectively. After tertiary treatment, water may be suitable for release directly to a water purification plant.
28.3 Concept Check Water treatment plants employ industrial-scale physical and chemical systems that remove or neutralize biological, inorganic, and organic contaminants from a variety of community and industrial wastewater sources. Water purification plants employ clarification, filtration, and disinfection processes to produce potable water. Finished potable water is free of chemical and biological contamination.
28.4 Concept Check Drinking water and recreational water may both be sources of waterborne pathogens. In the United States, the number of disease outbreaks due to either of these sources is relatively small in relation to the large number of exposures to water. Worldwide, lack of adequate water treatment facilities and access to clean water contributes significantly to the spread of infectious diseases.
28.5 Concept Check Vibrio cholerae is a pathogen that causes cholera, an acute diarrheal disease resulting in severe dehydration. Cholera occurs in pandemics. The current pandemic has endemic foci in the Americas, the Indian subcontinent, Asia, and Africa.
28.6 Concept Check Giardiasis and cryptosporidiosis are spread by the chlorine-resistant cysts of Giardia lamblia and Cryptosporidium parvum, respectively, in water contaminated by the feces of infected humans or animals. These diseases are occasionally propagated in drinking water and recreational water sources. Infection with either parasite causes diarrhea.
28.7 Concept Check Legionella pneumophila is a respiratory pathogen that causes legionellosis and Pontiac fever. L. pneumophila grows to high numbers in warm water and is spread via aerosols. The prevalence of legionellosis is not decreasing.
28.8 Concept Check Typhoid fever, viral infections, and amebiasis are important waterborne diseases. Waterborne typhoid fever and viral illnesses, while still common diseases in developing countries, have been controlled by effective water treatment in developed countries. Amebic dysentery caused by Entamoeba histolytica is a worldwide problem that affects millions of people. Meningoencephalitis is a rare but serious condition caused by Naegleria amebiasis.
