Health Effects of Drinking Water Contaminants

Health Effects of Drinking Water Contaminants

Prepared by:
Sandra A. Zaslow and Glenda M. Herman

Extension Housing Specialists


Published by: North Carolina Cooperative Extension ServicePublication Number: HE-393

Last Electronic Revision: March 1996 (JWM)

People are increasingly concerned about the safety of their drinking water. As improvements in analytical methods allow us to detect impurities at very low concentrations in water, water supplies once considered pure are found to have contaminants. We cannot expect pure water, but we want safe water.

The health effects of some contaminants in drinking water are not well understood, but the presence of contaminants does not mean that your health will be harmed. In North Carolina, drinking water is generally of high quality and free from significant contamination. Public water supplies are tested, and regulated to ensure that our water remains free from unsafe levels of contamination. Small private water supplies, including wells, are not regulated by drinking water standards, and the owner must take steps to test and treat the water as needed to avoid possible health risks.

What is in your drinking water? The only way to know is to have it tested.

Drinking water can become contaminated at the original water source, during treatment, or during distribution to the home.


  • If your water comes from surface water (river or lake), it can be exposed to acid rain, storm water runoff, pesticide runoff, and industrial waste. This water is cleansed somewhat by exposure to sunlight, aeration, and micro-organisms in the water.
  • If your water comes from groundwater (private wells and some public water supplies), it generally takes longer to become contaminated but the natural cleansing process also may take much longer. Groundwater moves slowly and is not exposed to sunlight, aeration, or aerobic (requiring oxygen) micro-organisms. Groundwater can be contaminated by disease-producing pathogens, leachate from landfills and septic systems, careless disposal of hazardous household products, agricultural chemicals, and leaking underground storage tanks.

Possible Health Effects

The levels of contaminants in drinking water are seldom high enough to cause acute (immediate) health effects. Examples of acute health effects are nausea, lung irritation, skin rash, vomiting, dizziness, and even death.

Contaminants are more likely to cause chronic health effects – effects that occur long after repeated exposure to small amounts of a chemical. Examples of chronic health effects include cancer, liver and kidney damage, disorders of the nervous system, damage to the immune system, and birth defects.

Evidence relating chronic health effects to specific drinking water contaminants is limited. In the absence of exact scientific information, scientists predict the likely adverse effects of chemicals in drinking water using human data from clinical reports and epidemiological studies, and laboratory animal studies.

Drinking Water Standards

The Safe Water Drinking Act of 1974 directed the U.S. Environmental Protection Agency (EPA) to ensure that public water systems (systems serving more than 25 people) and noncommunity water systems (hotels, campsites, restau- rants, migrant workers’ encampments, and work sites) meet minimum standards for protecting public health. Its main provisions directed the EPA to establish minimum drinking water standards to limit the amounts of various contaminants found in drinking water. Because of growing concerns about the safety of the water supply, amendments were made to strengthen this law in 1986. These amendments required the EPA to do the following:

  • Develop a maximum contaminant level goal (MCLG) and a maximum contarninant level (MCL) for all regulated contaminants. MCLGs are nonenforceable health-based goals and represent the maximum level of a contaminant that is expected not to cause any adverse health effects over a lifetime. MCLs are enforceable contaminant levels. They are set as close to the MCLG as possible and are based on protecting public health within economical and technical reason.
  • Increase the number of regulated contaminants to a total of 83 by June, 1989. MCLs must be set for an additional 25 contaminants every 3 years thereafter.
  • Set required schedules for water systems to monitor for contaminants in drinking water.
  • Identify best available technologies (BATS) for removing excess contaminants from water, based on efficiency, availability, and cost.
  • Issue variances and exceptions to systems that cannot comply with MCLs despite the application of BATS, unless an “unreasonable risk” to health exists. “Unreasonable risk” has not yet been defined.
  • Provide for public notification when drinking water standards are violated.
  • Ban the use of lead pipes, solder, fittings, and flux in public water systems.
  • Bolster enforcement of penalties for violators of drinking water standards at the state and local level.
  • Provide for protection of groundwater sources.

Contaminants are regulated when they occur in drinking water supplies and are expected to threaten public health. Most levels established by the EPA allow a sufficient margin of safety, but acceptable contaminant levels vary widely among individuals and population groups. For example, high sodium levels, harmless for most people, can be dangerous for the elderly, people with high blood pressure, pregnant women, and people having difficulty in excreting sodium.

North Carolina has adopted EPA standards and the state has responsibility for enforcing drinking water standards.

Risk Assessment

Every day, you can be exposed to combinations of many toxic substances and these substances may interact.

What is in water may represent only a small part of your overall exposure to a specific contaminant. Scientists who investigate how contaminants affect human health get information in several ways. They may study how a toxic substance has affected people in a community over time. In some cases, this can show relationship between exposure to a contaminant and a health effect They may also use animal studies to collect information on the acute and chronic health effects.

Research helps scientists determine toxic doses and levels below which toxic effects are not observed. For noncancer-causing toxic substances, scientists use “acceptable daily intake” to estimate risk. The acceptable daily intake is the amount of a contaminant or toxic substance that humans can consume daily for a lifetime without any known ill effects. It includes a margin of safety. For a cancer-causing substance, no safe level has been set. Toxicity is estimated by calculating a risk estimate, or the concentration of a substance that presents the least acceptable risk. In the case of cancer-causing toxins, regulations are based on a level of risk that is acceptable, not a safe amount or concentration of a substance.

Four Groups of Contaminants

Microbial Pathogens. Pathogens in drinking water are serious health risks. Pathogens are disease-producing micro-organisms, which include bacteria (such as giardia lamblia), viruses, and parasites. They get into drinking water when the water source is contaminated by sewage and animal waste, or when wells are improperly sealed and constructed. They can cause gastroenteritis, salmonella infection, dysentery, shigellosis, hepatitis, and giardiasis (a gastrointestinal infection causing diarrhea, abdominal cramps, and gas). The presence of coliform bacteria, which is generally a harmless bacteria, may indicate other contamination to the drinking water system.

Organics. People worry the most about potentially toxic chemicals and metals in water. Only a few of the toxic organic chemicals that occur drinking water are regulated by drinking water standards. This group of contaminants includes:

  • Trihalomthanes (THMs), which are formed when chlorine in treated drinking water combines with naturally occurring organic matter.
  • Pesticides, including herbicides, insecticides, and fungicides.
  • Volatile organic chemicals (VOCs), which include solvents, degreasers, adhesives, gasoline additives, and fuels additives. Some of the common VOCs are: benzene, trichloroethylene (TCE), styrene, toluene, and vinyl chloride. Possible chronic health effects include cancer, central nervous system disorders, liver and kidney damage, reproductive disorders, and birth defects.

Inorganics. These contaminants include toxic metals like arsenic, barium, chromium, lead, mercury, and silver. These metals can get into your drinking water from natural sources, industrial processes, and the materials used in your plumbing system. Toxic metals are regulated in public water supplies because they can cause acute poisoning, cancer, and other health effects.

Nitrate is another inorganic contaminant. The nitrate in mineral deposits, fertilizers, sewage, and animal wastes can contaminate water. Nitrate has been associated with “blue baby syndrome” in infants.

Radioactive Elements. Radon is a radioactive contaminant that results from the decay of uranium in soils and rocks. It is usually more of a health concern when it enters a home as a soil gas than when it occurs in water supplies. Radon in air is associated with lung cancer.


As people hear about the possibility of contaminants in their drinking water, they worry about potential health effects. Water supplies once considered to be pure may have various contaminants, often from natural sources. These are usually at levels below those considered to be harmful.

If you are concerned, test your water. For more information on water quality, testing, and treatment, contact the Extension Center or health department in your county or your physician.



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