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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 organisms 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 diseases are transmitted in the same ways. However, these diseases are more commonly spread from person to person or through ingestion of non-treated water. Recreational water such as streams, lakes and reservoirs are potential sources of crypto and giardia, which is why it is imperative to avoid drinking untreated or nonpotable water.

Children playing together can readily spread the disease to other children and their families through contact. Many infected people carry the parasites 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.

How does Denver Water control for giardia and cryptosporidium?

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 by enforcing more stringent water quality parameters then what is mandatory. 

Denver Water uses coagulation, flocculation, sedimentation, filtration and disinfection to target giardia and cryptosporidium. There is a video of this process on the Virtual Tour: Potable Water Treatment page. 

  1. Coagulation neutralizes charges on particles so they will come together. 
  2. Flocculation stirs together the coagulant particles to form larger particles. 
  3. Sedimentation is when the water flow is slowed down so that the larger particles settle out. 
  4. Filtration. Much like a coffee filter will keep the coffee grounds from passing into your cup of Joe, our granular filters attract and hold particles that did not settle out in the sedimentation basin.
  5. Disinfection is used to inactivate any cysts that may have made it through the first four steps. In accordance with regulations, a small amount of disinfectant is still present in water mains to keep water disinfected.