Water Information Center - Drinking Water Basics

Drinking Water Basics

Something in the Water? Water and Public Health

Water plays an essential role in sanitation and public health. But while it helps to keep people, homes, and cities clean, water itself can also carry harmful microbial or chemical contaminants. In the United States, many water quality regulations help to ensure that drinking water is adequately treated, monitored, and managed to protect public health. Nevertheless, some microbial and chemical contaminants still pose a threat.

Microbial Threats

During a two-week period in the spring of 1993, an estimated 403,000 people in Milwaukee, Wisconsin, became ill with stomach cramps, diarrhea, fever, and vomiting. The culprit: a microscopic parasite called Cryptosporidium parvum that had been insufficiently filtered from much of the city's water supply. Affecting more than a quarter of the city's residents and contributing to more than a hundred deaths, it was one of the largest documented waterborne disease outbreaks in modern U.S. history. The malfunctioning treatment plant was shut down following the outbreak, but the event stands as a reminder of the critically important role of effective water treatment.

Many waterborne diseases, including dysentery, typhoid, and cholera, have been virtually eradicated in the United States. Some waterborne bacteria, however—among them Legionella, Campylobacter, nontyphoid Salmonella, and pathogenic Escherichia coli—still cause illnesses. The CDC estimates that waterborne Legionella causes 8,000 to 18,000 illnesses each year in the United States. Legionella, the cause of Legionnaires' disease (discovered when an outbreak occurred at a Philadelphia convention of the American Legion in 1976), thrives in warm water. When inhaled through contaminated mist or vapor (for example, during showering), it causes pneumonia-like symptoms.

For more than 100 years, U.S. public health officials have relied on indicator organisms, coliform bacteria (found in the feces of humans and other animals), to detect microbial contamination in drinking water. Coliform tests are relatively inexpensive and widely used to test water for contamination.

However, the use of bacterial indicators does not always protect against other potentially harmful pathogens, such as viruses and single-celled organisms called protozoa (including Cryptosporidium parvum). Some of these pathogens survive in water much longer than coliform bacteria do, so a negative coliform test may not indicate an uncontaminated water sample. Scientists are at work to develop fast, sensitive, and inexpensive tests that look for other microbial contamination indicators in addition to coliform bacteria. Scientists have also called for expanding population health studies of waterborne disease outbreaks to better assess the sources of microbial contamination and prevent future outbreaks. For more information, see the National Research Council report Indicators for Waterborne Pathogens (2004).

Spotlight on Chlorine

Deaths from infectious disease have declined
sharply since utilities began using chlorine to
disinfect drinking water. Image courtesy of the
Marian Koshland Science Museum.Chlorine has been used routinely in U.S. public water systems for 100 years. Chlorine not only kills bacteria in the water at the treatment plant but also continues to disinfect all the way to the consumer's tap. When hurricanes Katrina and Rita struck the Gulf Coast in 2005, chlorinated disinfectants for sanitizing drinking water were among the critical emergency supplies that relief agencies brought in to help affected residents.

Disinfection by-products, which result from interactions between chlorinated disinfectants and naturally occurring organic matter in water, pose potential health problems in the liver, kidneys, or central nervous system, as well as an increased risk of cancer. Both chlorine and disinfection by-products are regulated by the EPA to protect public health.

Alternatives to chlorine disinfection include ozone and ultraviolet radiation; however, these approaches disinfect water only at the site of treatment, not throughout the distribution system. As a result, communities that use ozone or ultraviolet disinfection may add chlorine, or chlorine plus ammonia, as a final "secondary disinfectant" to provide protection throughout the distribution system.

Chemical Contaminants

A large array of synthetic organic chemicals have been released into the environment, and from there these chemicals can eventually find their way into drinking water supplies. Herbicides, pesticides, pharmaceuticals, antibiotics, industrial pollutants, and radioactive materials all present potential health threats in drinking water. Although these contaminants can be harmful, they are often present in drinking water at such a low concentration that they do not pose a health risk to consumers. The EPA is responsible for determining the highest acceptable concentrations of these contaminants in drinking water.

Case Study: Addressing Arsenic Poisoning in Bangladesh
Cupful by cupful, many people in Bangladesh are slowly being poisoned by their drinking water. Arsenic, a toxic chemical element, is found in the water of tens of millions of Bangladeshis at concentrations 10 to 50 times what is considered safe.

The contaminated water comes from tube wells that extract groundwater; arsenic has dissolved into the groundwater from natural sources. Bangladesh switched from using surface water to using groundwater relatively recently due to high levels of microbial contamination in surface water sources. Arsenic poisoning leads to several types of cancer and may also be linked to diabetes, respiratory and cardiovascular ailments, and birth defects. (Natural sources of arsenic exist in the United States,
Dr. Abul Hussam won the 2007 Grainger
Challenge Prize for his method for treating
arsenic-contaminated groundwater.
Image courtesy of Evan Cantwell,
George Mason University. but regulations set by the EPA make sure that arsenic concentrations in public sources of drinking water are kept well below harmful levels.) More information about arsenic in drinking water is available in the National Research Council report Arsenic in Drinking Water (2001).

To help address the serious public health problem arsenic poses in Bangladesh and other developing countries, the National Academy of Engineering held an engineering contest in 2007 to find a sustainable and economical water treatment system for arsenic-contaminated groundwater. The creators of the winning systems were awarded up to $1,000,000 (supported by The Grainger Foundation) for their innovative designs. The winning systems were required to be affordable, robust, reliable, easy to maintain, socially acceptable, and environmentally friendly. With further development and deployment in arsenic-affected areas, these new water treatment systems could well save lives.

Lead
In the mid-1990s, the District of Columbia Water and Sewer Authority (WASA) increased the dose of chlorine in Washington's water to better control microbial contamination. Later, WASA switched from using free chlorine to chloramines for final disinfection in order to lower the amount of potentially harmful disinfection by-products in the water.

Unfortunately, a serious unintended consequence of these changes—which were, ironically, implemented to protect public health—was later discovered. Increased concentrations of free chlorine, combined with pH variations and the conversion to chloramines, Lead in DC Water

had started a chemical reaction that caused lead from the city's and customers' pipes to leach into the water at consumers' taps. In 2002, more than 10 percent of sampled taps in residences in the nation's capital revealed lead contamination of up to 75 parts per billion—five times the EPA standard.

To comply with the Lead and Copper Rule of the Safe Drinking Water Act, Washington's water utility has taken several actions to address the city's lead contamination problems. First, it replaced 5,500 lead service lines in 2004-2005 and committed to replacing the public portion of all lead service lines by 2015. Homeowners were encouraged to replace lead pipes on their own property. Second, since August 2004, water treatment plants have been adding orthophosphate, a corrosion inhibitor, to the drinking water. This tasteless, odorless, food-grade additive can form a protective coating inside pipes, decreasing the amount of lead that leaches into the water from lead service lines and home plumbing systems.

The District of Columbia is not alone in facing problems with lead-contaminated drinking water. Prior to 1986, plumbing systems in most homes in America were built of copper pipes soldered together with lead. Unless the water chemistry is carefully controlled, lead can leach into tap water.

The EPA recommends that homeowners who suspect that there may be lead in their water have their water tested by a certified laboratory. Ingesting high levels of lead can cause delayed physical or mental development in infants and children, as well as kidney problems or high blood pressure in adults. The EPA estimates that 10 to 20 percent of lead exposure comes from contaminated drinking water; the majority of that contamination is caused by corroded pipes in homes and buildings.

Gasoline and Other Organic Contaminants
Petroleum hydrocarbons, including gasoline and other fuel oils, can enter groundwater through spills on the surface, leaking pipes or underground storage tanks, or intentional liquid waste disposal operations.

Overturned Storage Tank

A geologist notes the spilled contents of a
storage tank overturned during hurricanes
Katrina and Rita in 2005. Image courtesy of
the Aquifer Evaluation & Protection Section,
Louisiana Department of Environmental Quality.Chlorinated solvents, a family of chemicals used in some industrial processes and household consumer products, can also contaminate drinking water. Chlorinated solvents can be found in drain and oven cleaners, shoe polish, household degreasers, waxes, and pesticides. These solvents are also used in the aerospace and electronics industries, in dry cleaning products, and in some wood manufacturing processes. In 2006, the USGS reported on a study in which one in ten samples of drinking water across 12 states was found to contain trace concentrations of chlorinated solvents.

Cleaning up sites contaminated by petroleum hydrocarbons or the chemicals in chlorinated solvents can be challenging and expensive. One of the most promising approaches, bioremediation, involves the use of biological agents, such as bacteria or plants, to break down contaminants. Oil seeps occur naturally in some areas; as a result, some organisms have evolved enzymes to degrade

oil and related substances. Bioremediation technologies try to encourage the growth of such organisms in water contaminated by petroleum hydrocarbons.

Removing chlorinated solvents, on the other hand, presents a greater challenge. Because most chlorinated solvents are man-made, few organisms have the enzymes needed to degrade these chemicals. An additional challenge is how these contaminants behave in groundwater: while petroleum hydrocarbons tend to float, chlorinated solvents sink down to the bottom of an aquifer or into the bedrock that underlies it. For more information, see the National Research Council report Contaminants in the Subsurface: Source Zone Assessment and Remediation (2004).

Bottled or Tap?
Americans spent an estimated $16 billion on bottled water in 2007, guzzling a billion bottles each week. As bottled water becomes ever more popular—either because of its convenience or because people perceive it to be safer—many wonder: Is bottled water actually better than tap?

Some blind taste tests have given mixed results, with tasters often unable to tell the difference between tap and bottled water. Water quality standards are roughly comparable between the two, although some (including the Government Accountability Office) have criticized the methods used for testing the quality of bottled water. One key difference between bottled and tap water is that while most tap water contains fluoride to prevent tooth decay, bottled water generally does not.

Bottled water also costs several thousand times as much as tap water. Much of this markup goes into producing the bottle itself, as well as marketing and transportation costs. Producing all those bottles also comes with environmental consequences. The materials and processes used to make plastics and transport the products consume energy resources and can release pollutants into air and water. Furthermore, the used plastic bottles are often dumped into landfills rather than being recycled.

Because of water treatment processes, it is generally safe to drink tap water in every town and city in the United States. Some municipalities, such as New York City, have even launched advertising campaigns to increase trust in the city's water and decrease residents' use of bottled water.