The drinking-water supply comes from two sources, groundwater and surface water. In the developed world, most of the drinking-water supply is treated to remove solid contaminants by settling or filtration and some form of disinfection. It the developing world, drinking water often is used untreated directly from the source.
Access to safe, clean drinking water is a major public health concern worldwide. The World Health Organization (WHO) estimated that in 2010, about 780 million people lacked access to safe drinking water. Although the problem is most acute in the developing world, 120 million, or 15.4%, of these individuals lived in Europe. Good water quality is directly linked to the availability of effective sanitation systems. People who are least likely to have access to safe drinking water are those who live in rural areas, who live in poverty, and who live in a developing country.
Groundwater is brought up from under the earth by well pumps. Surface water is taken from sources open to the air such as lakes and rivers. Generally, surface water requires more treatment than groundwater. Water in public water systems can come from surface water, groundwater, or a combination of the two. Groundwater is the source of water in wells and most private water systems. Bottled water can come from either source.
By the 1700s, people were experimenting with other types of filters, including those made of wool and charcoal. Nevertheless, slow sand filtration was the most common form of early water treatment.
The first city water treatment plant was built in 1804 in Scotland, initiating the idea that all people should have access to clean, safe drinking water. More than 200 years later, that goal still was not reached.
As late as the mid-1800s, the drinking-water supply was not recognized as the source of many disease outbreaks. When a massive cholera outbreak occurred in London in late August 1854, within three days 127 people died. The death rate of those who became ill was about 12%. Before the outbreak was over, more than 600 people died.
John Snow, a physician, mapped the locations where cholera cases occurred. From this map, he deduced that cholera was caused by contaminated water. He convinced the municipal authorities to disable a public pump in the Soho area of London where the number of cholera cases was highest. Almost immediately, the cholera outbreak subsided in that area. Snow's map showed that most cholera cases clustered around city water pumps, whereas very few cases of cholera occurred in buildings with private wells. From this, Snow was able to show that cholera was caused by contamination of the water. Snow's discovery was a major event in public health history. It helped shift the focus of water treatment from taste and clarity to controlling waterborne pathogens.
Through the 1970s, drinking water treatment focused on removing disease-causing organisms from the water supply. Many cities used sand filtration, supplemented beginning in the early 1900s by the addition of disinfectant agents such as chlorine and ozone. Jersey City, New Jersey, was the first U.S. city to routinely add disinfectant to its municipal water supply.
In 1914, for the first time the U.S. Public Health Service set national drinking water standards for the amount of bacteria permitted in water. These standards only applied to water that crossed state lines (such as water on trains and ships) and applied only to organisms that caused disease. The standards were not adopted by all communities until the 1940s. By 1962, federal standards regulated 28 substances in drinking water.
By the 1970s, concern had increased about nonbiological contaminants in water. Fertilizer and pesticide use had increased, and runoff allowed these chemicals to enter lakes and streams and eventually the drinking-water supply. Other non-biological contaminants came from dumping of chemicals used in manufacturing, materials used in construction such as lead pipes, and chemicals that leached out of containers such as cans and bottles.
The Safe Drinking Water Act, passed in 1974, required the U.S. Environmental Protection Agency (EPA) to develop guidelines for the treatment and monitoring of public water systems. Since that time, several sets of amendments to the act have accelerated the regulation of contaminants, banned the use of lead pipe, and required surface water to be filtered and disinfected. The amendments also have provisions for greater groundwater protection. As of 2012, about 155,700 public water systems were covered by the act. These systems provided water for more than 95% of Americans.
The Safe Drinking Water Act only covers public and private systems that serve a minimum of 25 people at least 60 days a year. As of 2012, about 15 million Americans obtain their drinking water from privately owned wells that are not covered under the act. It is the responsibility of the well owners to have their wells regularly tested for contaminants. The act also does not apply to bottled water.
In the United States, the bottled water industry is not regulated by the EPA under the Safe Drinking Water Act or any other environmental law. Instead, the Food and Drug Administration (FDA) regulates bottled water under the Federal Food, Drug, and Cosmetic Act. Despite the image portrayed by advertising, studies indicate that bottled water is not any safer, in most cases, than tap water. Home water treatment units sometimes carry labels that claim they are EPA-approved, but these systems are not regulated either.
Water treatment and disinfection have eliminated most waterborne diseases in the developed world. For example, the rate of typhoid in the United States dropped from 100 cases per 100,000 population to one case per 1,000,000 in 2006. This drop is due primarily to disinfection of the drinking-water supply. The Centers for Disease Control and Prevention (CDC) and the National Academy of Engineers named water treatment as one of the greatest public health advances of the twentieth century. There is no debate that water treatment and disinfection have saved hundreds of thousands of lives in the developed world.
By contrast, according to the World Health Organization (WHO), in the developing world two million people die each year from diarrhea caused by unsafe water. Most of these are children under age five. Many more, especially children, are permanently damaged by the presence of toxic chemicals or parasites in the water.
There is a direct relationship between adequate sanitation facilities and safe drinking water. WHO estimates that more than one-third of the world's population has no access to adequate sanitation. WHO estimates that improved water safety, sanitation, and hygiene have the potential to prevent 6.3% of all deaths worldwide.
The drinking-water supply can become contaminated at many points: at the source of the water, through inadequate treatment (as often occurs after a natural disaster such as a hurricane), at water storage sites, and in the pipes that carry water to buildings. Drinking water can be contaminated by infectious agents (e.g., bacteria, viruses, parasites), toxic chemicals (e.g., pesticides, industrial chemicals), or radiological hazards (e.g., naturally occurring radon or radioactive waste from nuclear power plants). In the United States, most concerns about contamination center on toxic chemicals. There is debate about the amount of contaminants that should be permitted in the drinking-water supply and their effect on health. Some of these contaminants arise from natural sources (e.g., radon). Some enter the water system through runoff (e.g., pesticides), and others are byproducts of disinfectant chemicals (e.g., chlorine). Some, such as fluoride, are intentionally added to water to improve public health.
There is ongoing debate in the environmental and political communities about how to balance the health effects of drinking-water contaminants against the cost of their removal. It is impossible to remove all contaminants from water, so efforts are directed toward those that have the greatest demonstrable health effects. It should be noted that bottled water contains many of the same chemicals as tap water from the public water supply and that outbreaks of waterborne infections have occasionally been traced to bottled water.
The most common contaminants found in the public water supply in the United States are lead, nitrate, and radon, all of which pose health threats. Some studies suggest that substances such as chlorine and fluoride, which are added to water during the treatment process, may also have adverse effects on human health. The EPA sets standards for approximately 90 drinking-water contaminants.
Chlorine or a chlorine-based compound, which kills many disease-causing microbes, is now used to disinfect over 95% of the public water supply in the United States. While effective, chlorine reacts with organic compounds to form disinfection by-products (DBPs), which may increase the risk of certain kinds of cancer.
As of 2010, approximately 70% of Americans drawing drinking water from public water systems received fluoridated water. Fluoride exists naturally in some water, and bottled water may or may not contain fluoride depending on its source. It is also added to toothpastes and mouthwashes.
Critics of fluoridation still exist in the early twenty-first century. Some reject half a century of scientific research and claim that fluoridation is harmful. For others, fluoridation of public water raises moral issues about personal rights of versus the rights of government. The decision to fluoridate drinking water has generally rested with local governments and communities. The EPA limit for fluoride in water is 4 parts per million (ppm). The recommended concentration of fluoride in drinking water is between 0.7 and 1.2. The fluoridation rate is usually at the low end of the range in warm places and at the high end of the range in cold places, because people drink more water and thus get more fluoride where it is warm. High doses of fluoride are potentially toxic, and very large doses (5–15 times the daily adequate intake) taken over time cause bones to become chalky and brittle.
The allowable level of lead in the public drinkingwater supply was zero. This does not mean that all water is lead-free. Service pipes made of lead and leaded solder used on copper plumbing and brass faucets are the main sources of lead in water. Acidic or soft water increases the danger of lead contamination because it corrodes the plumbing and leeches out the lead. About 80% of homes have water that is moderately to highly acidic. In 1993, the EPA required all large public water companies to reduce the corrosiveness of water by adding calcium oxide or other hardening agents. Depending on exposure, lead poisoning can cause permanent learning disabilities, behavioral and nervous system disorders, and severe brain damage.
Vegetables, drinking water, and meat preservatives are the main sources of nitrates and nitrites in the human diet. There is a link between nitrate and gastric cancer. Nitrate is converted to nitrite by bacteria in the mouth and stomach, and this is in turn converted into N-nitroso compounds, which have been proved carcinogenic in laboratory animals. Nitrates can be found in fertilizer runoff. They are a common contaminant of wells in agricultural areas.
Most water-treatment plants in the United States use chemical coagulation to remove impurities and contaminants. Aluminum sulfate is often added to the water, causing some contaminants to coagulate with the aluminum and precipitate out. The majority of the aluminum left in the water is removed by subsequent treatment processes, but a residual amount passes through the system to the consumer. Aluminum has been linked with neurotoxicity, specifically Alzheimer's disease, but no causal relationship has been established and this link seems increasingly unlikely.
The organic chemicals that are found most frequently in drinking water are pesticides, trichloreothylene, and trihalomines. Pesticides usually make their way into drinking water through seepage and runoff in agricultural areas. In high doses, they can damage the liver, the kidneys, and the nervous system, as well as increase the risk of various cancers. Trichloreothylenes are industrial solvents, and the populations at highest risk from this chemical have a water supply located near hazardous waste sites. The health risks associated with trichloreothylenes are nervous system damage and cancer. Chlorination of water that is contaminated with organic matter is responsible for the formation of trihalomethanes in water, and studies suggest that they may increase cancer rates.
See also Chlorination ; Cholera ; Disease outbreaks ; Fluoridation ; Hazardous waste ; Lead poisoning ; Ozone ; Parasites ; Safe Drinking Water Act ; Sanitation ; Water quality .
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Centers for Disease Control and Prevention (CDC), 1600 Clifton Rd., Atlanta, GA, 30333, (404) 639-3534, (800) CDC-INFO (800-232-4636); TTY: (888) 232-6348, firstname.lastname@example.org, http://www.cdc.gov .
National Institute of Environmental Health Science, PO Box 12233, MD K3-16, Research Triangle Park, NC, 27709, (919) 541-1919, Fax: (919) 541-4395, http://www.niehs.nih.gov .
UNICEF Headquarters, 2 United Nations Plaza, New York, NY, 10017, (212) 326-7000, Fax: (212) 887-7465, http://www.unicef.org .
United States Environmental Protection Agency, 1200 Pennsylvania Ave. NW, Washington, DC, 20460, (202) (202) 272-0165, http://water.epa.gov .
World Health Organization, Avenue Appia 20, 1211 Geneva 27, Switzerland, +4122 791 21 11, Fax: +4122 791 31 11, email@example.com, http://www.who.int .
Tish Davidson, AM