Giardia and Drinking Water from Private Wells

What is giardiasis?

Giardiasis (GEE-are-DYE-uh-sis) is a diarrheal illness caused by a microscopic parasite, Giardia intestinalis (also known as Giardia lamblia or Giardia duodenalis). Once an animal or person is infected with Giardia, the parasite lives in the intestine and is passed in feces. Because the parasite is protected by an outer shell, it can survive outside the body and in the environment for long periods of time (i.e., months).

During the past 30 years, Giardia infection has become recognized as a common cause of waterborne disease in humans in the United States. Giardia can be found worldwide and within every region of the United States.

How can I become infected with Giardia?

Giardia may be found in soil, food, water, or surfaces that have been contaminated with feces from infected humans or animals. You can become infected after accidentally swallowing the parasite. Giardia is not spread by contact with blood.

Where and how does Giardia get into drinking water?

Millions of Giardia parasites can be released in a bowel movement of an infected human or animal. Feces from these humans or animals can get into your well through different ways including sewage overflows, polluted storm water runoff, and agricultural runoff.

What are the symptoms of giardiasis?

Giardia infection can cause a variety of intestinal signs or symptoms, which include:

• Diarrhea
• Gas or flatulence
• Greasy stools that tend to float
• Stomach or abdominal cramps
• Upset stomach or nausea

These symptoms may lead to weight loss and dehydration. Some people with Giardia infection have no symptoms at all. Symptoms of giardiasis normally begin 1 to 2 weeks (average 7 days) after becoming infected.

What should I do if I think I have giardiasis?

See your health care provider to discuss your concerns.

How is a Giardia infection diagnosed?

Your health care provider will likely ask you to submit stool samples to check for the parasite. Because Giardia can be difficult to diagnose, your provider might ask you to submit multiple stool specimens collected over a few days.

What is the treatment for giardiasis?

Several prescription drugs are available to treat Giardia infection. Although Giardia can infect all people, young children and pregnant women might be more susceptible to dehydration resulting from diarrhea and should, therefore, drink plenty of fluids while ill. Rapid loss of fluids from diarrhea can be especially life threatening to infants. Therefore, parents should talk to their health care providers about fluid replacement therapy options for infants.

How can I remove Giardia from my drinking water?

Heat the water to a rolling boil for at least 1 minute (at altitudes greater than 6,562 feet [>2,000 meters], boil water for 3 minutes). Water should then be stored in a clean container with a lid and refrigerated.

An alternative to boiling water is using a point-of-use filter. Not all home water filters remove Giardia. Filters that are designed to remove the parasite 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.

Although Giardia is larger than one micron in size, filters with pore sizes of absolute one micron can filter out Giardia as well as Cryptosporidium. To search for certified products, please visit NSF International, and click "cyst reduction" in the drop down menu under "reduction claim." Then select the type of product to search (e.g. "faucet mount") and look for certified products.

As you consider ways to disinfect your well, it is important to note that Giardia is moderately chlorine resistant. Contact your local health department for recommended procedures. Remember to have you well water tested regularly after disinfection to make sure the problem does not happen again.

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