Over 15 million U.S. households obtain their drinking water from private wells 1, which are not covered by the United States Environmental Protection Agency (EPA) regulations that protect public drinking water systems. Although the United States has one of the safest drinking water supplies in the world, sources of drinking water can still become contaminated through naturally occurring chemicals and minerals (for example, arsenic, radon), local land use practices (for example, pesticides, chemicals, animal feeding operations), malfunctioning wastewater treatment systems (for example, sewer overflows), and other sources. Contamination of a private well can impact not only the household served by the well, but also nearby households using the same aquifer.
Top 6 Causes – Outbreaks in Individual (Private) Water Systems – Wells
Top Causes of Outbreaks in Wells*
- Hepatitis A
- Campylobacter, E. coli (tie)
- Cryptosporidium, Salmonella (tie)
- Arsenic, Gasoline, Nitrate, Phenol, Selenium (tie)
For a complete listing of water-related surveillance data, see CDC’s Surveillance Reports for Drinking Water-associated Disease & Outbreaks.
Owners of private wells are responsible for ensuring that their water is safe from contaminants. Private wells should be checked every year for mechanical problems, cleanliness, and the presence of coliform bacteria, nitrates, and any other contaminants of local concern. A local health department or water well systems professional can help ensure delivery of high-quality water from an existing well or, if needed, help locate and construct a new well in a safer area. Additional information about well maintenance and water testing is available at Healthy Water’s Well Testing page.
The presence of contaminants in water can lead to health issues, 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.
More information about specific germs or chemicals and drinking water from private wells can be found on their individual pages linked from the top of this page.
For more water-related diseases, see CDC Healthy Water’s Alphabetical Index of Water-related Health Data.
- U.S. Census Bureau. Current Housing Reports, Series H150/07, American Housing Survey for the United States: 2007.[PDF – 642 pages] U.S. Government Printing Office. Washington, DC: 20401, Printed in 2008.
*1971-2010; Ordered from highest to lowest frequency (i.e., #1 is the most-commonly reported etiology). Several etiologies were reported only once, resulting in a ‘Top 6’ list. 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. Excludes outbreaks with multiple or unknown water sources (e.g., well and spring, well and lake/river, unknown ground water). Does not include historic legionellosis outbreaks reported in the 2007-2008 data summary due to missing drinking water system information.