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INTRODUCTION

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A clean and adequate supply of drinking water is vital to life and good health. Adequate supplies are also needed for agriculture and sustainable development. Because of differing distributions of freshwater worldwide and differing weather patterns and droughts, many parts of the world suffer from inadequate supplies. In other areas, supplies are abundant, but contamination or pollution makes them unsafe for drinking or agriculture. More recently, there is concern that global warming may add increasing pressures to the ability of countries to maintain safe and adequate water supplies. Freshwater consumption has tripled over the last 50 years, and demand for water to sustain the world's people is projected to double by 2025. By that date, nearly half the estimated world's population of more than 6 billion will be living in countries where either the quantity or the quality of water supplies will have sunk to levels ranging from inadequate to economically crippling.

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BIOCONTAMINATION OF WATER SUPPLIES

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Biocontamination of water supplies used or intended for human drinking water represents the most immediate waterborne threat to human health. Nearly 80% of diseases in developing countries are associated with water, causing some 3 million early deaths. A growing understanding of the epidemiologic characteristics and patterns of disease associated with human pathogens distributed in drinking water has led to the development of infrastructure for potable and waste water collection, storage, treatment, disinfection, and distribution in the urban areas of most developed countries. As the microbiologic integrity of the supply of potable water has improved, a significant reduction in human disease caused by waterborne pathogens has occurred. Nonetheless, recent experience has demonstrated that the potable water supply throughout the world is always at risk. Serious waterborne disease epidemics with recognized and new pathogens continue to occur in both developed and developing areas of the world.

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Worldwide, explosive population growth, expanding poverty, urban migration, and increased international travel affect the risk of exposure to waterborne infectious disease. These emerging diseases include waterborne cryptosporidial diarrheal disease and cholera, Escherichia coli 0157:H7 diarrheal disorders, Mycobacterium avium complex, Legionella species, Helicobacter pylori, and Cyanobacteria species. Cyclospora species, Cryptosporidia, and Giardia continue to be parasitic threats to potable water supplies. Coccidia and other protozoans are common food- and waterborne pathogens throughout the world. Toxoplasmosis has been identified as a result of waterborne Toxoplasma gondii. Hemorrhagic fevers, tuberculosis, and hantavirus infections may have waterborne sources. Municipal drinking water supplies can also be contaminated by viruses both from surface waters and from unidentified sources. These viruses include hepatitis A, enteroviruses, echoviruses, coxsackie viruses, Norwalk virus, rotavirus, caliciviruses, and adenoviruses.

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The most common effect of waterborne biocontamination is acute diarrheal disease. This disease is characterized by loose or watery stools, and it is often accompanied by vomiting and fever. Many of these diarrheal episodes are the result of waterborne infection with bacteria, viruses, or parasites or the ingestion of ...

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