Report on the Environment
Drinking Water Quality
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What are the trends in the condition of drinking water and their effects on human health?
The average American consumes 1 to 2 liters of drinking water per day, including water used to make coffee, tea, and other beverages.25 Virtually all drinking water in the United States comes from fresh surface water and ground water. Large-scale water supply systems tend to rely on surface water resources such as lakes, rivers, and reservoirs; these include the systems serving many large metropolitan areas. Smaller systems are more likely to use ground water, particularly in regions with limited surface water resources. Slightly more than half of the nation’s population receives its drinking water from ground water, i.e., through wells drilled into aquifers26 (including private wells serving about 15 percent of U.S. households27). If drinking water contains unsafe levels of contaminants, this contaminated water can cause a range of adverse human health effects. Among the potential effects are gastrointestinal illnesses, nervous system or reproductive effects, and chronic diseases such as cancer.
Surface waters and aquifers can be contaminated by various agents, including microbial agents such as viruses, bacteria, or parasites (e.g., E. coli, Cryptosporidium, or Giardia); chemical contaminants such as inorganic metals, volatile organic compounds (VOCs), and other natural or manmade compounds; and radionuclides, which may be manmade or naturally occurring. Contaminants also can enter drinking water between the treatment plant and the tap (for example, lead can leach into water from old plumbing fixtures or household or street-side pipes).
Drinking water contaminants can come from many sources:
- Human activities that contaminate the source. Aquifers and surface waters that provide drinking water can be contaminated by many sources, as discussed in Sections 3.2 and 3.3. For example, chemicals from disposal sites or underground storage facilities can migrate into aquifers; possible contaminants include organic solvents (e.g., some VOCs), petroleum products, and heavy metals. Contaminants can also enter ground water or surface water as a result of their application to the land. Pesticides and fertilizer compounds (e.g., nitrate) can be carried into lakes and streams by rainfall runoff or snowmelt, or percolate through the ground and enter aquifers. Industrial wastes can contaminate drinking water sources if injected into containment wells or discharged into surface waters, as can mine waste (e.g., heavy metals) if not properly contained.
- Natural sources. As ground water travels through rock and soil, it can pick up naturally occurring contaminants such as arsenic, other heavy metals, or radionuclides. Some aquifers are naturally unsuitable for drinking because the local geology happens to include high levels of certain contaminants.
- Microbial pathogens. Human wastes from sewage and septic systems can carry harmful microbes into drinking water sources, as can wastes from animal feedlots and wildlife. Major contaminants include Giardia, Cryptosporidium, and E. coli O157:H7. Coliform bacteria from human and animal wastes also may be found in drinking water if the water is not properly finished; these bacteria may indicate that other harmful pathogens are present as well.
- Treatment and distribution. While treatment can remove many chemical and biological contaminants from the water, it may also result in the presence of certain disinfection byproducts that may themselves be harmful, such as trihalomethanes. Finished water can also become contaminated after it enters the distribution system, either from a breach in the system or from corrosion of plumbing materials, particularly those containing lead or copper. After water leaves the treatment plant, monitoring for lead in drinking water is done at the tap, and monitoring for microbial contaminants (as well as disinfection byproducts) occurs within the distribution system.
Chemical exposure through drinking water can lead to a variety of long- and short-term effects. Potential health effects of exposure to certain metals, solvents, and pesticides can include chronic conditions such as cancer, which can develop over long periods of time (up to 70 years). Higher doses over shorter periods of time can result in a variety of biological responses, including toxicity, mutagenicity, and teratogenicity (birth defects). Short-term results might include cosmetic effects (e.g., skin discoloration), unpleasant odors, or more severe problems such as nervous system or organ damage and developmental or reproductive effects. The effects of some drinking water contaminants are not yet well understood. For example, certain disinfection byproducts have been associated with cancer, developmental, and reproductive risks, but the extent of this association is still uncertain.
Consuming water with pathogenic microbes can cause life-threatening diseases such as typhoid fever or cholera—rare in the U.S. today—as well as more common waterborne diseases caused by organisms such as Giardia, Cryptosporidium, E. coli, and Campylobacter. Health consequences of the more common illnesses can include symptoms such as gastrointestinal distress (stomach pain, vomiting, diarrhea), headache, fever, and kidney failure, as well as various infectious diseases such as hepatitis.
A number of factors determine whether the presence of contaminants in drinking water will lead to adverse health effects. These include the type of contaminant, its concentration in the water, individual susceptibility, the amount of contaminated water consumed, and the duration of exposure.
Disinfection of drinking water—the destruction of pathogens using chlorine or other chemicals—has dramatically reduced the incidence of waterborne diseases such as typhoid, cholera, and hepatitis, as well as gastrointestinal illness, in the United States. Other processes required depend on the physical, microbiological, and chemical characteristics and the types of contaminants present in the source water (e.g., filtration to remove turbidity and biological contaminants, treatment to remove organic chemicals and inorganic contaminants such as metals, and corrosion control to reduce the presence of corrosion byproducts such as lead at the point of use).