The United States has one of the safest public drinking water supplies in the world. Over 286 million Americans get their tap water from a community water system (1). The US Environmental Protection Agency (EPA) regulates drinking water quality in public water systems and sets maximum concentration levels for water chemicals and pollutants.
Sources of drinking water are subject to contamination and require appropriate treatment to remove disease-causing contaminants. Contamination of drinking water supplies can occur in the source water as well as in the distribution system after water treatment has already occurred. There are many sources of water contamination, including naturally occurring chemicals and minerals (for example, arsenic, radon, uranium), local land use practices (fertilizers, pesticides, concentrated feeding operations), manufacturing processes, and sewer overflows or wastewater releases.
The presence of contaminants in water can lead to adverse health effects, including gastrointestinal illness, reproductive problems, and neurological disorders. Infants, young children, pregnant women, the elderly, and people whose immune systems are compromised because of AIDS, chemotherapy, or transplant medications, may be especially susceptible to illness from some contaminants.
Top 10 Causes – Outbreaks in Public Water Systems*
- Giardia
- Legionella
- Norovirus
- Shigella
- Campylobacter
- Copper
- Salmonella
- Hepatitis A
- Cryptosporidium
- E. coli, excess fluoride (tie)
For a complete listing of water-related surveillance data, see CDC’s Surveillance Reports for Drinking Water-associated Disease & Outbreaks.
*1971-2010; Ordered from highest to lowest frequency (i.e., #1 is the most-commonly reported etiology). Calculations include etiologic agents from outbreaks with multiple etiologies. Excludes outbreaks with known contamination at point of use (Deficiency 11A, etc.), unless non-POU outbreak deficiencies were also listed. Does not include historic legionellosis outbreaks reported in the 2007-2008 data summary due to missing drinking water system information.
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