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Cryptosporidium (Crypto) and Drinking Water from Private Wells


What is cryptosporidiosis?

Cryptosporidiosis ((krip-toh-spore-id-ee-OH-sis), is a diarrheal disease caused by a microscopic parasite, Cryptosporidium, that can live in the intestine of humans and animals and is passed in the stool of an infected person or animal. Both the disease and the parasite are commonly known as "Crypto." The parasite is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine-based disinfectants. During the past 2 decades, Crypto has become recognized as one of the most common causes of waterborne disease (recreational water and drinking water) in humans in the United States. The parasite is found in every region of the United States and throughout the world.

For more information about cryptosporidiosis and treatment, please CDC's cryptosporidiosis website.


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Where and how does Crypto get into drinking water?

Crypto is found in every part of the United States and throughout the world. Millions of Crypto can be released in a bowel movement from an infected human or animal. Crypto may be found in water sources such as private wells that have been contaminated with feces from infected humans or animals. Water can be contaminated through sewage overflows, sewage systems that are not working properly, polluted storm water runoff, and agricultural runoff. Wells may be more vulnerable to such contamination after flooding, particularly if the wells are shallow, have been dug or bored, or have been submerged by floodwater for long periods of time.


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How can I find out whether there is Cryptosporidium in my drinking water?

If you suspect a problem and your drinking water comes from a private well, you may contact your state certification officer for a list of laboratories in your area that will perform tests on drinking water for a fee.


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How do I remove Crypto from my drinking water?

To kill or inactivate Crypto, bring your water to a rolling boil for one minute (at elevations above 6,500 feet, boil for three minutes) Water should then be allowed to cool, stored in a clean sanitized container with a tight cover, and refrigerated.

An alternative to boiling water is using a point-of-use filter. Not all home water filters remove Crypto. Filters that are designed to remove Crypto should have one of the following labels:

  • Reverse osmosis,
  • Absolute pore size of 1 micron or smaller,
  • Tested and certified by NSF Standard 53 for cyst removal, or
  • Tested and certified by NSF Standard 53 for cyst reduction.

To learn more about treatment, visit CDC’s A Guide to Water Filters page.

You may also disinfect your well. However, it is important to note that Crypto is extremely tolerant of chlorination, making chlorination an ineffective intervention. Alternative disinfection processes to consider include systems that utilize ultraviolet light or ozone. Contact your local health department for recommended procedures. Remember to have your well water tested regularly, at least once a year, after disinfection to make sure the problem does not recur.


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