Giardia – Its Effects, How to Test for It, and How to Treat It

Giardia effects – According to the EPA’s Giardia fact sheet: Giardia (je-ar’de-ah) are protozoan parasites which occur in a trophozoite and an oval-shaped cyst form.  They are commonly excreted in the feces of an infected host, after which they can move freely through the environment. Infection is transmitted when these excreted cysts are ingested by another suitable host.

So where is it found?  Acccording to the EPA, Giardia is almost always found in municipal waters and surface water supplies.  It is distributed through lakes, ponds, rivers, streams, while “the wide occurrence of cysts in humans and animals suggests that soil can be contaminated with Giardia through fecal deposition and sewage disposal practices. ”

Giardia is highly infective, and has an incubation period of anywhere from 3 to 25 days. Once infection occurs, symptoms can include diarrhea, abdominal cramps, bloating, gas, weight loss, and vomiting.  While Giardia rarely causes death, “each year 4,600 persons with giardiasis are estimated to be hospitalized in the United States,” according to the EPA.

While the EPA does not enforce a Maximum Contaminant Level for Giardia, it has set a Maximum Contaminant Level Goal (the level below which a contaminant is deemed safe for ingestion) of zero.

Testing for Giardia is best accomplished by sending a sample of your water to a laboratory. Both our Home Water Well Test Kit and Well Water Home Test Kit come with a pre-paid mailer for sending your water sample back to our lab for analysis.

As the EPA’s Giardia fact sheet notes, “cysts are relatively more resistant to disinfectants [e.g. chlorine] than bacteria and viruses, and high doses and lengthy contact times may be needed.”  For this reason, Giardia is best treated with a UV sterilizer, reverse osmosis system, or distiller.  Some filters, like the Doulton Rio, can also trap Giardia cysts and remove them from your water supply.

About the Author Gerry Bulfin

Need help with your well water? I have been assisting homeowners, small communities and businesses improve their well water quality since 1989. Please email me at if you have a question about water testing, test kits or well water systems in general. Gerry Bulfin CWS-IV Master Water Specialist WQA Certified Licensed California Water Treatment Contractor