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Fluoridated Water: Questions and Answers 

1. What is fluoride? 

Fluoride is the name given to a group of compounds that are composed of the naturally 

occurring element fluorine and one or more other elements. Fluorides are present 

naturally in water and soil. 

2. What is fluoridated water? 

Virtually all water contains some amount of fluoride. Water fluoridation is the process of 

adding fluoride to the water supply so that the level reaches approximately 1 part fluoride 

per million parts water (ppm) or 1 milligram fluoride per liter of water (mg/L); this is the 

optimal level for preventing tooth decay (1). 

3. Why fluoridate water? 

In the early 1940s, scientists discovered that people who lived where drinking water 

supplies had naturally occurring fluoride levels of approximately 1.0 ppm had fewer 

dental caries (cavities). Many more recent studies have supported this finding (1). 

Fluoride can prevent and even reverse tooth decay by enhancing remineralization, the 

process by which fluoride “rebuilds” tooth enamel that is beginning to decay (1, 2). 

Key Points 

• Fluoride prevents and can even reverse tooth decay (see Question 3). 

• More than 60 percent of the U.S. population on public water supply 

systems has access to water fluoridated at approximately 1 part fluoride 

per million parts water—the optimal level for preventing tooth decay 

(see Question 4). 

• Many studies, in both humans and animals, have shown no association 

between fluoridated water and risk for cancer (see Question 5). 
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4. When did water fluoridation begin in the U.S.? 

In 1945, Grand Rapids, Michigan, adjusted the fluoride content of its water supply to 

1.0 ppm and thus became the first city to implement community water fluoridation. By 

1992, more than 60 percent of the U.S. population served by public water systems had 

access to water fluoridated at approximately 1.0 ppm, the optimal level to prevent tooth 

decay (2). 

The Centers for Disease Control and Prevention (CDC) considers fluoridation of water 

one of the greatest achievements in public health in the 20th century. 

5. Can fluoridated water cause cancer? 

The possible relationship between fluoridated water and cancer has been debated at 

length. The debate resurfaced in 1990 when a study by the National Toxicology 

Program, part of the National Institute of Environmental Health Sciences, showed an 

increased number of osteosarcomas (bone tumors) in male rats given water high in 

fluoride for 2 years (3). However, other studies in humans and in animals have not 

shown an association between fluoridated water and cancer (4). 

In a February 1991 Public Health Service (PHS) report, the agency said it found no 

evidence of an association between fluoride and cancer in humans. The report, based on 

a review of more than 50 human epidemiological (population) studies produced over the 

past 40 years, concluded that optimal fluoridation of drinking water “does not pose a 

detectable cancer risk to humans” as evidenced by extensive human epidemiological data 

reported to date (4). 

In one of the studies reviewed for the PHS report, scientists at the National Cancer 

Institute evaluated the relationship between the fluoridation of drinking water and the 

number of deaths due to cancer in the United States during a 36-year period, and the 

relationship between water fluoridation and number of new cases of cancer during a 

15-year period. After examining more than 2.2 million cancer death records and 125,000 

cancer case records in counties using fluoridated water, the researchers found no 

indication of increased cancer risk associated with fluoridated drinking water (5). 

In 1993, the Subcommittee on Health Effects of Ingested Fluoride of the National 

Research Council, part of the National Academy of Sciences, conducted an extensive 

literature review concerning the association between fluoridated drinking water and 

increased cancer risk. The review included data from more than 50 human 

epidemiological studies and six animal studies. The Subcommittee concluded that none 

of the data demonstrated an association between fluoridated drinking water and cancer 

(5). A 1999 report by the CDC supported these findings. The report concluded that 

studies to date have produced “no credible evidence” of an association between 

fluoridated drinking water and an increased risk for cancer (2). 
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6. Where can people find additional information on fluoridated water? 

The CDC Web site has information on standards for and surveillance of current 

fluoridated water supplies in the United States. Visit http://www.cdc.gov and search for 

“fluoridation.” 

The Environmental Protection Agency (EPA) Web site has more information about 

drinking water and health. It includes information about drinking water quality and 

standards. This Web site is located at http://www.epa.gov/safewater/ on the Internet. 

Selected References 

1. Centers for Disease Control and Prevention. Public Health Service report on fluoride 

benefits and risks. Journal of the Americal Medical Association 1991; 266(8):1061–

1067. 

2. Centers for Disease Control and Prevention. Achievements in public health, 1900–1999: 

Fluoridation of drinking water to prevent dental caries. Morbidity and Mortality Weekly 

Report 1999; 48(41):933–940. 

3. Bucher JR, Hejtmancik MR, Toft JD, et al. Results and conclusions of the National 

Toxicology Program’s rodent carcinogenicity studies with sodium fluoride. International 

Journal of Cancer 1991; 48(5):733–737. 

4. Committee to Coordinate Environmental Health and Related Programs. Review of 

Fluoride Benefits and Risks: Report of the Ad Hoc Subcommittee on Fluoride. Public 

Health Service, Department of Health and Human Services, 1991. 

5. National Research Council. Carcinogenicity of flouride. In: Subcommittee on Health 

Effects of Ingested Fluoride, editor. Health Effects of Ingested Fluoride. Washington 

DC: National Academy Press, 1993. 

# # # 

Related Resources

Publications (available at http://www.cancer.gov/publications) 

• Cancer and the Environment 

• What You Need To Know AboutTM Cancer 
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National Cancer Institute (NCI) Resources

Cancer Information Service (toll-free)

 Telephone: 1–800–4–CANCER (1–800–422–6237) 

 TTY: 1–800–332–8615 

Online 

NCI’s Web site: http://www.cancer.gov 

LiveHelp, NCI’s live online assistance: 

https://cissecure.nci.nih.gov/livehelp/welcome.asp

 

This fact sheet was reviewed on 6/29/05