Safety of Water

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Safety of Water

The understanding that some water caused disease while other water sources did not has long prompted human civilizations to attempt to make water safe to drink. Sanskrit medical lore from around 2000 B.C.E. mentions boiling foul water, exposing it to sunlight, and filtering through charcoal. It is possible that the Asian custom of drinking tea made with boiling water was an early method to make water safe to drink. Cyrus the Great in the sixth century B.C.E. took vessels of boiled water with his troops when they traveled to do battle. Residents of Alexandria, Egypt in 50 B.C.E. drank Nile River water brought to the city through a series of underground aqueducts to cisterns where it was clarified by sedimentation. Other parts of the Egyptian empire used single, double, and even triple filtration to purify water. Sextus Julius Frontinus, water commissioner of Rome in 97 C.E., wrote the first detailed description of a public water system in his Two Books on the Water Supply of the City of Rome. While these early water engineers had no understanding of bacteria and were probably treating water to decrease its cloudiness and improve its looks and taste, they nevertheless developed the earliest water treatment systems.

In one of the earliest cases to link a specific disease to the water supply, Dr. John Snow demonstrated in 1855 how cholera spread through water pumps during a large outbreak of the disease in London. He noticed that people who obtained their water from a particular well were more likely to become ill than those drawing their water from another well. He persuaded city officials to remove the pump handle from that particular well, forcing inhabitants to draw water from another well, and the number of cholera cases dropped immediately.

The U.S. Water Supply

In 1799 Philadelphia became the first U.S. city with a public water system that pumped water from a surface source and distributed it through a series of pipes to residents. By 1900 there were more than 3,000 public water systems in the United States. Rather than guaranteeing a safe water supply, some of those systems actually contributed to major disease outbreaks in the early 1900s. If the water supplies were contaminated, the pumped and widely distributed water provided a means for spreading bacterial disease throughout communities. Federal regulation of the nation's drinking water began in 1914 when the U.S. Public Health Service (PHS) imposed bacteriological standards for drinking water. These standards were revised in 1925, 1946, and 1962 and were eventually adopted by all fifty states. After World War II, industrialization and the use of fertilizers on crops began to pollute the quality and safety of the nation's water. A 1969 survey showed that only 60 percent of water systems delivered water that met PHS standards. A study in 1972 detected thirty-six chemicals present in already treated water taken from the Mississippi River. This increased awareness of the problems with the water supply led to the passage of federal environmental and health laws dealing with polluted water, hazardous waste, and pesticides.

Current water use in the United States averages about 100 gallons per person per day, more than just about any other country. A very small proportion of this, approximately two gallons, is actually used for drinking and cooking. Drinking water comes from either surface water or groundwater. Surface water includes rivers, lakes, and reservoirs, while groundwater is pumped up from wells drilled into aquifers, underground geologic formations that contain water. Over half the nation gets its drinking water from groundwater sources.

The more than 170,000 water systems in the United States are either private or public. Private water systems do not draw water from a public water supply and serve only one or a few homes. Public water systems include community water systems and those at schools, factories, campgrounds, and some restaurants that have their own water supply. Community water systems deliver water to people year-round in their homes. In most community water systems, a network of underground pipes transports water under pressure to smaller pipes that then enter individual homes.

Hazards to the Water Supply and Treatment Methods

Because water is the universal solvent, many chemicals and other materials easily dissolve in it. Water supplies become contaminated through many different channelschemicals can migrate from disposal sites; animal wastes and pesticides may be carried to lakes and streams by rainfall runoff; human wastes may be discharged to receiving waters that ultimately flow into water used for drinking. Other sources of contamination include discharge from industry, erosion of natural deposits, corrosion of household plumbing systems, and leaching from septic tanks. Nitrates, inorganic compounds that can enter water supplies from fertilizer runoff and sanitary wastewater discharges, are especially harmful to young children. Naturally occurring contaminants are also found in drinking water. For example, the radioactive gas radon-222 occurs in certain types of rock and can seep into groundwater. It would be impossible to remove all contaminants from our water supply. It would also be unnecessary since at very low levels many contaminants are generally not harmful.

Most outbreaks of waterborne disease are due to contamination by bacteria and viruses, mostly from human or animal waste. Two pathogens commonly associated with drinking water are Cryptosporidium parvum and Giardia lamblia. Both are protozoa that cause gastrointestinal illness and have cysts that are difficult to destroy. Cryptosporidium in particular may pass through water treatment filtration and disinfection processes in sufficient numbers to cause health problems. Cryptosporidium was first documented as posing a threat of infection to humans in 1976. A 1993 outbreak of cryptosporidiosis in Milwaukee, Wisconsin, is the largest outbreak of waterborne disease to date in the United States. Milwaukee's water supply, which comes from Lake Michigan, is treated by filtration and disinfection. Due to an unusual combination of circumstances during a period of heavy rainfall and runoff, water treatment was ineffective. An estimated 403,000 persons were affected by the disease, 4,400 were hospitalized, and at least 50 died. The original source of contamination is still unknown. Although Cryptosporidium had previously been found in surface water, it was not expected to appear in treated water from a municipal water supply that met state and federal standards for acceptable water quality. Increased awareness of the parasite has led to increased testing for it, and, not surprisingly, increased prevalence has been discovered. In addition to drinking-water outbreaks, Cryptosporidium is associated with swimming pools and amusement park wave pools. This is particularly important as Cryptosporidium is highly resistant to chlorine and other chemical disinfectants. This is a new parasite showing up in new environments with new resistance capabilities.

Runoff from farms is another source of hazards to the nation's drinking water. In 1994 the Environmental Working Group released Tap Water Blues, a report in which the group identified over ten million individuals who had been exposed to five herbicides at levels above the Environmental Protection Agency's (EPA) negligible cancer risk standard of one additional case per million individuals. A second report in 1995, Weed Killers by the Glass, analyzed herbicides in the tap water of twenty-nine Midwestern cities. Again, their results show that Americans are exposed to harmful pesticides in their drinking water at levels far above federal health standards.

The Centers for Disease Control (CDC), the EPA, and the Council of State and Territorial Epidemiologists collaborate to maintain a surveillance system that collects data on waterborne disease outbreaks (WBDOs) from drinking and recreational water. This program seeks to determine what pathogens in the water supply cause illness, how many people become ill, and how and why outbreaks occur. The data are submitted on a voluntary basis and most likely underestimate the true incidence of WBDOs. More WBDOs occur in the summer months, and the cause is often unidentified. WBDO outbreaks peaked between 1979 and 1983 and have been declining ever since. This decrease could be due to improved implementation of water treatment regulations, increased efforts by many water utilities to produce drinking water substantially better than EPA standards require, and efforts by public-health officials to improve drinking-water quality. Of the waterborne disease outbreaks reported to the CDC from 1974 to 1996, about 12 percent were caused by bacterial agents, 33 percent by parasites, 5 percent by viruses, 18 percent by chemical contaminants, and 31 percent by unidentified agents.

During 1997 and 1998 there were seventeen outbreaks in drinking water, resulting in 2,038 people becoming ill. Six (35.3 percent) of the illnesses were caused by parasites (4 by Giardia, 2 by Cryptosporidium); four (23.5 percent) by bacteria (three by E. coli O157:H7 and one by Shigella sonnei ); five (29.4 percent) were of unidentified origin; and two (11.8 percent) were attributed to chemical poisoning. Both chemical poisonings were from copper. Eight (47.1 percent) of the seventeen WBDOs were associated with community water systems. Of these eight, three were caused by problems at water treatment plants, three were the result of problems in the water distribution systems and plumbing of individual facilities, and two were associated with contaminated, untreated groundwater. Five (29.4 percent) of the seventeen WBDOs were associated with noncommunity water systems; all five were from groundwater (i.e., a well or spring) systems. The four outbreaks (23.5 percent) associated with individual water systems were also from groundwater.

Also during 1997 and 1998, eighteen outbreaks associated with recreational water caused 2,138 people to become ill. Nine (50 percent) were caused by the parasite Cryptosporidium. The other outbreaks were due to E. coli O157:H7 (three outbreaks or about 16.7 percent), Shigella sonnei (one outbreak or 5.6 percent), Norwalk-like viruses (two outbreaks or 11.1 percent), and unknown causes (three outbreaks or 16.7 percent). Slightly over half (55.6 percent) occurred in treated waterpools, hot tubs, or fountains; the others occurred in fresh-water lakes, rivers, or hot springs.

Depending on the conditions and types of contaminants likely to be found in a particular water source, most water suppliers use a combination of two or more treatment processes. Major water treatment processes are:

Flocculation/sedimentation. Flocculation is the process of getting small particles to combine into heavier particles called floc. The heavier particles can then be removed by letting them settle out as sediment. Once settled, the particles combine to form a sludge that is later removed.

Filtration. Filtration removes particles from water by passing the water through a permeable fabric or porous bed of materials. Groundwater is naturally filtered as it flows through porous layers of soil. Some filtration processes can remove very small particles, including microorganisms.

Ion exchange. Ion exchange processes remove inorganic constituents such as arsenic, chromium, excess fluoride, nitrates, radium, and uranium if they cannot be removed adequately by filtration or sedimentation. Electric current is used to attract negative and/or positive ions to one side of a treatment chamber for removal.

Adsorption. Adsorption involves making organic contaminants that cause undesirable color, taste, or odor stick to the surface of granular or powdered activated carbon.

Disinfection. Disinfection refers to killing harmful microorganisms. The three most commonly used methods of disinfection are chlorination, ozonation, and ultraviolet treatment. Chlorination is the method most often used in the United States while ozonation is very common in Europe.

Chlorination. Chlorine kills bacteria by forming hypochlorus acid, which attacks the respiratory, transport, and nucleic acid activity of bacteria. Most bacteria are very susceptible to chlorine while viruses are less so. Cysts from Giardia lamblia are very resistant to chlorine, and Cryptosporidium cannot be readily killed by chlorination. Of concern with this method of disinfection are the by-products (DBPs), particularly trihalomethanes (THMs), formed when chlorine reacts with organic matter that is in the water. Long-term exposure to some DBPs may increase the risk of cancer or have other adverse health effects. THMs are cancer group B carcinogens, which means they have been shown to cause cancer in laboratory animals. EPA regulations limit the amount of these by-products allowed in drinking water.

Ozonation. Ozone is created by passing air through an electric current. The ozone gas is then dissolved in water, where it acts as an oxidant to destroy microorganisms. The ozone is removed before the water is used. As there is no residual antimicrobial effect, it is still necessary to chlorinate the water after ozone treatment. Ozone has received increased attention because it appears to be the only disinfectant that is effective against Cryptosporidium.

Ultraviolet light. Ultraviolet light (UV) does not actually kill bacteria. Instead, it effectively sterilizes them, making it impossible for them to reproduce. The use of ultraviolet light is only practical for small water systems due to the need for the microorganisms to be close to the radiation source. UV does not inactivate Giardia or Cryptosporidium cysts.

With so many different bacteria that can cause illness, it is not possible to test the water supply for each of them separately. Instead, indicator organisms are used. Coliform bacteria are the most popular indicator organisms for drinking water as they are easily detected in water. Coliforms are a group of bacteria common in the environment and in the digestive tracts of humans and animals. While these organisms are themselves harmless, their presence indicates possible contamination with human and/or animal waste. The effectiveness of disinfection is judged by analyzing water supplies for total coliform bacteria. Presence of coliform bacteria is not acceptable in public water supplies and is a sign that disinfection is required.


Local governments, public water systems, the states, and the EPA work together to ensure that all public water supplies are safe. Local governments have a direct interest in protecting the quality of their drinking-water source, be it groundwater or surface water. Part of the governments' job in protecting the water supply is to oversee land uses that can affect the quality of untreated source water. State public health and environmental agencies have the primary responsibility for ensuring that federal drinking-water quality standards, or more stringent ones required by the state, are met by each public water supplier. Municipal water systems test their own water systems for residues but do not regulate or test private wells. For households on private wells, state and local health departments usually have some standards for the drinking water, but it is generally up to the homeowner to maintain the quality of the drinking water.

An increased awareness of the vulnerability of the nation's water supply led to the passage of the 1974 Safe Drinking Water Act (SDWA). Prior to 1974 each state ran its own drinking-water program and set local standards. As a result, drinking-water protection standards differed from state to state. The act authorized the EPA to establish national enforceable health standards for contaminants in drinking water, encouraged federal-state partnerships in protecting the nation's water supply, and required notification to alert customers to water-system violations. In 1986 the act was strengthened through the Surface Water Treatment Rule, which requires public water systems to filter and disinfect all surface-water supplies. In 1996 amendments to the act extended the protection of drinking water from source to tap. Provisions in the 1996 amendment include the following:

  • Consumers must receive more information about the quality of their drinking-water supplies. Water suppliers must notify customers within twenty-four hours of violations of EPA standards "that have the potential to have serious adverse effects on human health as a result of short-term exposure." If such a violation occurs, the system must announce it through the media and provide information about potential adverse effects on human health, steps taken to correct the violation, and the need to use alternative water supplies (such as boiled or bottled water) until the problem is corrected. When microorganisms such as those that indicate fecal contamination are found in drinking water, water suppliers may be required to issue "boil water notices." At least 725 communities, including New York City and the District of Columbia, have issued boil water notices affecting over 10 million people.
  • The SDWA amendments also require public water systems to prepare Consumer Confidence Reports. These are to inform consumers about the source of their water supply, contaminant levels detected in their water, and the health effects of contaminant levels that are above the established safety limit. Beginning in 1999, systems are to prepare and distribute the reports annually.
  • Under the new amendments, each state must develop a program to identify potential contamination threats and determine the susceptibility of drinking-water sources to activities that may harm the source water.
  • The 1996 SDWA Amendments provides up to $9.6 billion over six years to improve drinking-water infrastructure. Water systems can apply for low-and no-interest loans to upgrade their facilities and ensure compliance with drinking-water standards. Other sources of funding are also available to water systems through the U.S. Department of Agriculture's Rural Utility Service (RUS). As part of the Water 2000 initiative, which is aimed at providing clean, safe, and affordable drinking water to all rural homes, RUS administers a water and wastewater loan and grant program. Under the RUS programs, rural areas and small cities and towns can receive loans or grants to restore a deteriorating water supply, upgrade a water or wastewater facility, or develop new systems.
Sample monitoring schedule
Contaminant Minimum monitoring frequency
Acute Contaminants 
Bacteria Monthly or quarterly, depending on system size and type
Protozoa and Viruses Continuous monitoring for turbidity, monthly for total coliforms, as indicators
Nitrate Annually
Chronic Contaminants 
Volatile Organics (e.g., benzene) Groundwater systems, annually for two consecutive years; surface water systems, annually
Synthetic Organics (e.g. pesticides) Larger systems, twice in three years; smaller systems, once in three years
Inorganics/Metals Groundwater systems, once every three years; surface water systems, annually
Lead and Copper Annually
Radio nuclides Once every four years
General requirements may differ slightly based on the size or type of the drinking-water system.
SOURCE: Environmental Protection Agency (EPA). July 1997. Water on Tap: A Consumer's Guide to the Nation's Drinking Water. Washington, D.C.: Environmental Protection Agency, Office of Water, 1997. Available at

The EPA Office of Water sets standards for pesticides and other chemicals in drinking water and issues Maximum Contaminant Levels (MCLs), which limit the amount of each substance that can be present in drinking water, for more than eighty contaminants. Scientists use a process called risk assessment to set drinking-water quality standards. When assessing the cancer and non-cancer risks from exposure to a chemical in drinking water, the first step is to measure how much of the chemical could be in the water. Next, scientists estimate how much of the chemical the average person is likely to drink. This amount is called the exposure. In developing drinking-water standards, the EPA assumes that the average adult drinks two liters of water each day throughout a seventy-year life span. MCLs are set at levels that will limit an individual's risk of cancer from that contaminant to between one in 10,000 and one in 1,000,000 over a lifetime. For non-cancer effects, risk assessment provides an estimate of an exposure level below which no adverse effects are expected to occur. The EPA also takes into account the ability of various technologies to remove the contaminant, their effectiveness, and the cost of treatment.

To comply with MCLs, public water systems may use any state-approved treatment. According to 1996 statistics, 7 percent of community water systems, or 4,151 systems, reported one or more MCL violations, and less than 2 percent (681 systems) reported violations of treatment technique standards. The table shows the major groups of contaminants and the minimum frequency with which water systems must test for them.

Finally, Healthy People 2010, a national health-promotion and disease-prevention initiative, has two goals for water quality:

  1. Increase the proportion of persons served by community water systems who receive a supply of drinking water that meets the regulations of the Safe Drinking Water Act. The current baseline is 73 percent; 2010 goals are to increase that to 95 percent.
  2. Reduce waterborne disease outbreaks from drinking water among persons served by community water systems. Currently an estimated six outbreaks per year originate from community water systems. The goal is to decrease that to two outbreaks per year.

See also Food Safety .


Baker, M. N. The Quest for Pure Water: The History of Water Purification from the Earliest Records to the Twentieth Century. New York: American Water Works Association, 1948.

Carson, Rachel. Silent Spring. Boston: Houghton Mifflin, 1962.

Environmental Protection Agency (EPA). 25 Years of the Safe Drinking Water Act: History and Trends. Washington: Environmental Protection Agency, December 1999. Available at

Environmental Protection Agency (EPA). Water on Tap: A Consumer's Guide to the Nation's Drinking Water. Washington: Environmental Protection Agency, July 1997. Available at

Environmental Working Group (EWG). Just Add Water. Washington: Environmental Working Group, May 1996. Available at

Environmental Working Group (EWG). Weed Killers by the Glass. Washington: Environmental Working Group, September 1995. Available at

Food and Drug Administration. What Guidance Does FDA Have for Manufacturers of Bottled Waters? Available at

Frerichs, Ralph R. Snow on Cholera. Part 2: Broad Street Pump Outbreak. Internet slide show. Los Angeles: UCLA School of Public Health, 1999. Available at

Government Printing Office. Code of Federal Regulations, 21CFR165.110, pp. 521537. Bottled water. Available at

International Bottled Water Association. The IBWA Model Code. 2000. Available at

National Drinking Water Clearinghouse. Tech Briefs. Morgan-town, W.Va.: National Drinking Water Clearinghouse, 1996-1999.

Natural Resources Defense Council. Bottled Water: Pure Drink or Pure Hype? March 1999. Available at

Cynthia A. Roberts

Bottled water

As news reports of contaminated municipal water supplies proliferate, more and more Americans are purchasing bottled water. Between 1976 and 1997 yearly sales of bottled water skyrocketed from 500,000 gallons to almost 3.5 million gallons. Even though the cost of bottled water is 240 to 10,000 times more per gallon than that of tap water, the industry continues to grow at a rate of 8 to 10 percent per year. Many people buy bottled water with the assumption that it is safer than regular tap water.

Bottled water is considered a food and as such is regulated by the FDA under the Code of Federal Regulations Title 21, Part 165, Section 110. FDA considers carbonated water and seltzer water to be soft drinks, and thus regulates them as such. FDA regulations only apply to products that are sold in interstate commerce. Therefore, FDA does not regulate bottled waters that are packaged and sold within the same state, an estimated 60 to 70 percent of all bottled water sold in the United States. States regulate bottled water to varying degrees. One-fourth of bottled water is actually bottled tap water, which may or may not be further treated. EPA regulates tap water.

In its 1999 report, Bottled Water: Pure Drink or Pure Hype?, the Natural Resources Defense Council (NRDC) found that, while most of the bottled waters they tested were of high quality and safe, some brands were contaminated. The NRDC also believes that EPA regulations governing tap water are more stringent than the FDA regulations for bottled water. The NRDC concluded that bottled water is not always safer than tap water.

FDA has also established current good manufacturing practice (CGMP) regulations for processing and bottling drinking water, which apply to all waters sealed in bottles, packages, or other containers. Under the CGMP regulations for bottled water, the water to be bottled must be from an approved source and must be processed, packaged, transported, and stored under safe and sanitary conditions. The International Bottled Water Association has also produced a voluntary model code for use by its members.