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Crypto & Giardia

Denver Water has tested for Cryptosporidium (Crypto) and Giardia in raw and treated water since the 1980s. We have never detected a viable indication of either in treated drinking water.

Crypto and Giardia are microscopic organisms that, when ingested, can cause diarrhea, cramps, fever and other symptoms. They are usually spread through means other than drinking water.

Where do the parasites come from?

Both come from the intestinal tracts of warm-blooded animals. Many of these animals — such as elk, deer, beaver, and muskrats — live in the Rocky Mountains. Others live in our own homes or yards, including dogs, cats and mice.

Animal waste can find its way into a stream or lake and the environmentally-resistant cysts present in the waste are carried downstream. A human or animal who drinks this untreated water may develop the disease. Ingesting as few as 10 cysts can give someone giardiasis.

How do you get giardiasis and cryptosporidiosis?

Giardiasis is the more common illness of the two, but both these diseases are transmitted in the same ways. However, these diseases are more commonly spread from person to person. Children playing together contact can readily spread the disease to other children and their families. Many infected people carry the parasite without showing any symptoms.

Both parasites can also be foodborne. An infected food handler who does not use proper sanitation can transmit the disease.

Giardia can also be passed directly from an infected animal (wild or domestic) to a person.

Are these parasites in drinking water?

If cysts are in the raw water that enters the treatment plant, the application of disinfectant will kill many of them. In one treatment step, polymers and other chemicals are added to the water to help remove dirt particles. The water is then filtered, and any cysts should be removed with the dirt and chemical residue. In accordance with regulations, a small amount of disinfectant is still present in water mains to keep water disinfected.

Cryptosporidium is more resistant to common treatment methods like heat and disinfection, but it can be controlled by exposure to ultraviolet light and through reverse osmosis filtration. Monitoring of our raw water indicates no need for such costly measures.

The federal government requires compliance with certain standards of treatment designed to prevent these parasites from contaminating drinking water, and Denver Water complies with those regulations. Outbreaks involving other municipal water supplies were usually caused by improper treatment or system failures.