Protozoa are one-celled, microscopic organisms that are larger than bacteria and are found in soil and water. There are many types of them that are beneficial in the environment, but some types of protozoa can cause diseases when consumed through contaminated water.
Two types of protozoa, Cryptosporidium and Giardia lamblia, are listed as primary contaminants by the US EPA because any amount of these protozoa in your drinking water can have potential health effects. It is important to ensure that well water is properly treated and disinfected to remove any potential protozoa.
A close up of Giardia. / © Adobe Stock
What are the effects of protozoa in well water?
The presence of some protozoa in water can pose health risks. Drinking water contaminated with these microorganisms may cause gastrointestinal illnesses such as diarrhea, vomiting, and abdominal cramps. It is important to note that the symptoms may vary depending on the individual’s immune system.
When should I test for protozoa in my well water?
Signs of protozoa in well water may not be apparent through visual inspection, taste, or smell. The only way to reliably determine if your well water is contaminated with these microbes is to have a sample analyzed by a certified laboratory. If someone who drinks your well water becomes sick and tests positive for a protozoa that poses health risks, you should have your water tested.
To ensure you are protecting your family’s health, we have developed a set of recommendations for testing that are provided in our article, "What do I need to know about sampling my well water?"
What treatment should I use if there are protozoa in my well water? How do I remove protozoa from my water?
Once you test and need to treat your water to remove protozoa, there are effective methods including continuous chlorination, distillation, ultraviolet (UV) treatment, and ozonation. For more information, the Minnesota Department of Health has developed a Home Water Treatment Guide that covers treatment for any common constituent in well water. The most important advice we can provide you is if you are going to add treatment to your home water system, be sure the treatment device has been certified to remove iron by an independent third-party certification organization.
Where can I get local help and information about protozoa in my well water?
Contact your local health department – They can help you interpret your sample results and may have information on the best treatment options for your situation. If they personally aren’t able to answer your questions, they will know who to contact who will be able to help you, likely at your state health department.
State or Federal Geologic or Water Resource Agency – They may have completed field studies of your area or collected samples from water wells to map and understand the water quality in your state. In addition, they may house water well logs (including yours), or be able to provide additional information about the aquifer your well is getting water from.
Consult your well driller or drilling contractor – The contractor that drilled your well, or other local contractors, may be aware of the water quality issues nearby, including protozoa, and might have worked with other well owners in your area to solve this issue.
Research online – You should be inquisitive; it will help you significantly because there may be great information available online. Use search terms like “my state (CA, ME, IL, etc.) water well logs”, “my state groundwater quality”, or “my state well water quality”.
Contact us directly – If these other local sources don’t work out for you, we may be able to help. We may be able to provide direct assistance, and/or direct you to a technical assistance provider in your area who can help answer your questions (This is a free service funded by the US EPA).
Additional Resources
Cryptosporidium. 2023. Minnesota Department of Health.
Giardia: Drinking Water Fact Sheet. 2000. Office of Water. US Environmental Protection Agency.
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