Drinking-Water Supply

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Drinking-water supply

The Safe Drinking Water Act , passed in 1974, required the Environmental Protection Agency (EPA) to develop guidelines for the treatment and monitoring of public water systems. In 1986, amendments to the act accelerated the regulation of contaminants, banning the future use of lead pipe, and requiring surface water from most sources to be filtered and disinfected. The amendments also have provisions for greater groundwater protection. Despite the improvement these regulations represent, only public and private systems that serve a minimum of 25 people at least 60 days a year are covered by them. Millions obtain their drinking water from privately owned wells that are not covered under the act.

Drinking water comes from two primary sources: surface water and groundwater. Surface water comes from a river or lake, and groundwater, which is pumped from underground sources, generally needs less treatment. Contaminants can originate either from the water source or from the treatment process.

The most common contaminants found in the public water supply are lead, nitrate, and radonall of which pose substantial health threats. Studies indicate that substances such as chlorine and fluoride which are added to water during the treatment process may also have adverse effects on human health. Over 700 different contaminants have been found in water supplies in the United States, yet the EPA has only established maximum containment levels for 30 of them. Drinking water enforcement has been severely limited at both the state and federal levels. In 1990, 38,000 public water systems committed over 100,000 violations of the act, yet state governments only took legal enforcement action against 1,000, and the federal government took action against only 32. In only 6% of these cases were customers informed of the violations.

Chlorinated water was first used in 1908 as a means of reducing diseases in Chicago stockyards. Chlorination , which kills some disease-causing microbes , is now used to disinfect approximately 75% of the water supply in the United States. Numerous studies conducted over the past 20 years have found that chlorine reacts with organic products such as farm runoff or decaying leaves to form byproducts that increase the risk of certain kinds of cancer . These by-products of chlorination are associated with cancer of the bladder and of the colon, probably because both store concentrated waste products. Research released by the Medical College of Wisconsin suggests that drinking chlorinated water increases the risk of bladder cancer by 20% and the risk of rectal cancer by 38%. Despite the correlation between chlorination by-products and these types of cancer, many still believe that the benefits of chlorine disinfection outweigh the risks. Some hope this study will prompt those in charge of public water systems to investigate other methods of disinfection, such as the use of ozone or exposure to ultraviolet light, both of which are currently used in Europe.

The effectiveness of fluoridated water in reducing dental cavities was first noted in communities with a naturally occurring source of fluoride in their drinking water, and controlled studies of communities where fluoride was added to the water confirmed the results. As of 1989, residents in 70% of all cities with populations greater than 100,000 were drinking fluoridated water. The EPA limit for fluoride in water is 4 parts per million (ppm), and most cities add only one ppm to their water. Fluoridated water also has adverse effects, and these may include immune system suppression, tooth discoloration, undesirable bone growth, enzyme inhibition, and carcinogenesis.

The EPA has set the acceptable level of lead in drinking water at 15 parts per billion (ppb), yet according to tests the agency has done, drinking water in almost 20% of cities in the United States exceeds that limit. The EPA has estimated that 25% of a child's lead intake comes from drinking water, and it cautions that the percentage could be much higher if the water contains high levels of lead. Depending on exposure, lead poisoning can cause permanent learning disabilities, behavioral and nervous system disorders, as well as severe brain damage and death. 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. As of January 1, 1993, EPA regulations require all large public water companies to reduce the corrosiveness of water by adding calcium oxide or other hardening agents.

Chlorination and government standards for drinking water quality have virtually eliminated the outbreak of the classic water-borne diseases such as cholera , typhoid, and malaria . According to The American Journal of Public Health, however, recent studies have shown that water that meets current drinking water standards can still contain organisms which cause gastrointestinal (GI) disease. In a 15-month study conducted by the University of Quebec in Montreal, researchers equipped 299 homes with reverse-osmosis water filters , which remove bacterial and chemical contaminants. Over 600 families participated in the study, about half with the filters and half without them, and they were asked to keep records of all GI illnesses among household members. During this 15 month period, the households equipped with the water filters had 35% fewer incidents of GI illness and diarrhea. In 1992, The New England Journal of Medicine published a study showing that drinking water can harbor the bacterium that causes Legionnaire's disease. Some patients diagnosed with Legionnaire's disease were infected with the same type of Legionella pneumophila that was found in samples of their drinking water.

Vegetables, drinking water, and meat preservatives are the main sources of nitrates and nitrites in our diet. There is a definite 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 proven highly carcinogenic in laboratory animals. Bottle-fed infants are at additional risk, because once the nitrate is converted to nitrite in the stomach it combines with fetal hemoglobin and converts to methaemoglobin. When 10% of the hemoglobin has been converted, cyanosis or blue-baby syndrome occurs; and when 70% of the hemoglobin is in methaemoglobin form, death occurs. According to a recent EPA report, half of the private wells in the United States contain nitrate.

Radioactivity occurs naturally and it can be present in drinking water. Preliminary studies have linked it to increased rates of leukemia and cancers of the bladder, breast, and lungs. The EPA has established 5 picocuries per liter (pCi/L) as the safe limit for radium in drinking water. An estimated 1001,800 deaths per year are attributed to radon in tap water. According to EPA estimates over eight million people have excessively high radon levels in their water supply. Unlike most contaminants found in water, radon does not have to be ingested to pose a health hazard; dish washing, showering, or just running the faucet can agitate the water and release the radon into the air. According to EPA estimates, there are 10,00040,000 lung-cancer deaths each year from radon inhalation. Radon is most frequently a problem in New England, North Carolina, and Arizona, and it is most likely to be found in well water and small water systems. Most large treatment facilities disperse radon during the treatment process.

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 in drinking water has been linked with neurotoxicity, specifically Alzheimer's disease.

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, and in high doses they can damage the liver, the kidney, and the nervous system, as well as increase the risk of various cancers. Trichloroethylene are industrial wastes and the populations at highest risk from this chemical have a water supply located near hazardous waste sites. The health risks associated with trichloroethylene 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 preliminary studies suggest that it may increase cancer rates.

The bottled water industry is not sufficiently regulated, and it does not guarantee water purity. Despite the image portrayed by advertising, studies indicate that bottled water is not any safer in most cases than tap water. Home treatment units carry labels which frequently claim they are EPA-approved, but these are not regulated either. Different types of water filters are capable of removing different contaminants, so most experts recommend that anyone planning to install a treatment system have their water tested first.

Though scientific evidence clearly demonstrates that drinking water can be a health hazard, some of the most effective measures are also the easiest to implement. Studies have found that letting tap water run for several minutes reduces the lead content of the water by up to 70%. Companies that supply drinking water can be monitored by requesting copies of their test results and reporting any violations to the EPA. Lobbying for more stringent regulations is widely considered an effective tool for ensuring safe drinking water. Reduction of pesticide use and additional measures implemented for the protection of groundwater and surface water would also greatly reduce many of these health risks.

See also Carcinogen; Communicable diseases; Filtration; Groundwater pollution; Hazardous waste siting; Neurotoxin; Toxic substance; Water pollution; Water quality standards; Water resources; Water treatment

[Debra Glidden ]



Felsenfield, A., and M. A. Roberts. "A Report of Fluorosis in the United States Secondary to Drinking Well Water." Journal of the American Medical Association 265 (23/30 January 1991): 486-8.

Stout, J., et al. "Potable Water as a Cause of Sporadic Cases of Community-Acquired Legionnaires' Disease." New England Journal of Medicine 326 (16 January 1992): 151-5.


Packham, R. F. "Chemical Aspects of Water Quality and Health." Annual Symposium of the Institution of Water and Environmental Management. London, England: IWEM, 1990.