Availability of Water Resources
Closely associated with the overall availability of water resources is the problem of water pollution and human diseases. At present, approximately 20% of the world’s population lack safe drinking water, and nearly half the world population lack adequate sanitation. This problem is acute in many developing countries that discharge an estimated 95% of their untreated urban sewage directly into surface waters. For example, of India’s 3119 towns and cities, only 8 have full wastewater treatment facilities. Downstream, the untreated water is used for drinking, bathing, and washing, resulting in serious human infections and illnesses.
Overall, waterborne infections account for 90% of all human infectious diseases in developing countries. Lack of sanitary conditions contributes to approximately 12 million deaths each year, primarily among infants and young children. Flooding accounts for about half of the major disasters affecting humans each year.
Approximately 40% of U.S. fresh water is deemed unfit for recreational or drinking water uses because of contamination with dangerous microorganisms, pesticides, and fertilizers. In the U.S., waterborne infections account for approximately 940,000 infections and approximately 900 deaths each year. In recent decades, more U.S. livestock production systems have moved closer to urban areas, causing water and foods to be contaminated with manure. In the U.S., the quantity of livestock manure and other wastes produced each year are estimated to be 1.5 billion tons. Associated with this kind contamination, the Communicable Disease Center reports that more than 76 million Americans are infected each year with pathogenic E. coli and related food-borne pathogens, resulting in about 5,000 deaths per year.
The incidence of schistosomiasis, which is also associated with contaminated freshwater, is expanding worldwide and each year infects more than 200 million people and currently causes an estimated 20,000 deaths per year. Its spread is associated with an increase in habitats, including the construction of dams and irrigation canals suitable for the snail intermediate-host population and accessible for humans to come in contact with the infected water . For example, construction of the Aswan High Dam in Egypt and related irrigation systems in 1968 led to an explosion in Schistosoma mansoni in the human population; increasing from 5% in 1968 to 77% of all Egyptians in 1993. In 1986, the construction of a dam in Senegal resulted in an increase in schistosomiasis from zero per cent in 1986 to 90% by 1994.
Mosquito-borne malaria is also associated with water bodies. Worldwide this disease presently infects more than 2.4 billion people and kills about 2.7 million each year. Environmental changes, including polluted water, have fostered this high incidence and increase in malaria. For instance, deforestation in parts of Africa exposes land to sunlight and promotes the development of temporary pools of water that favor the breeding of human-biting, malaria-transmitting mosquitoes, Anopheles gambiae. In addition, with many African populations doubling every 20 years, more people are living in close proximity to mosquito infested aquatic ecosystems. Concurrently, the mosquito vectors are evolving resistance to insecticides that pollute their aquatic ecosystems, while protozoan pathogens are evolving resistance to the over-used antimalarial drugs. Together these factors are reducing the effectiveness of many malaria control efforts.
Transmitted via Air
Another serious water-borne infectious disease that can be transmitted via air, water, and food, is tuberculosis. At present, approximately 2 billion people are infected with TB with the number increasing each year.
In the Worldwide
Presently, worldwide about 2 billion people are infected with one or more helminth species, either by direct penetration or by use of contaminated water or food. In locations where sanitation is poor and overcrowding is rampant, as in parts of urban Africa, up to 90% of the population may be infected with one or more helminthes.
In addition to helminthes and microbe pathogens, there are many chemicals that contaminate water and have negative impacts on human health as well as natural biota. For example, an estimated 3 billion kg of pesticides are applied worldwide each year in agriculture. USEPA also allowed the application of sludge to agricultural land and this sludge is contaminated with heavy metals and other toxics. Many of these agricultural chemicals, including nitrogen fertilizer, contaminate aquatic ecosystems by leaching and runoff and result in eutrophication of aquatic ecosystems and other environmental problems. Worldwide, pesticides alone contribute to an estimated 26 million human poisonings and 220,000 deaths each year.