What's on Tap: Parasitic Cysts: Cryptosporidium and Giardia


Cryptosporidium and giardia are common intestinal parasites that cause flu-like illnesses. They are not bacteria or viruses, but protozoa with complex life cycles, which exist in a cyst form, similar to a microscopic egg. Cryptosporidium "cannot be seen without a very powerful microscope", says WebMD and "is so small that over 10,000 of them would fit on the period at the end of this sentence." Giardia cysts are also extremely small, 10 times smaller than the smallest object that can be seen with the naked eye.


Both are commonly transmitted through drinking water that hasn't been cleaned or treated. When even just a few cysts are consumed, they enter the small intestine, where they exist, and "hatch," and can multiply into millions of protozoa. Animals, including pets, are also carriers and can easily pick up cysts in water. Livestock are notorious carriers of cryptosporidium, while beavers have been identified as a carrier of giardia. Once in the water, both types of cysts can infect a host for months, especially in colder water where they are more resistant to natural die-off.


According to the Mayo Clinic, "when cryptosporidia enter your body, they travel to your small intestine and then burrow into the walls of your intestines. Later, cryptosporidia are shed in your feces." Symptoms of cryptosporidia are similar to the stomach flu and can include watery diarrhea, dehydration, lack of appetite, weight loss, stomach cramps or pain, fever, nausea and vomiting. It usually goes away within a week or two, but cryptosporidium can be life-threatening if you have a compromised immune system and don't get proper medical treatment. One of the most common causes of waterborne disease in the United States, giardia can live in the intestines of humans and animals for 2 to 6 weeks sometimes longer. A person can be infected with and even spread giardia without ever experiencing symptoms, and it can take up to three weeks after exposure for them to develop. The Mayo Clinic lists the most common symptoms as "watery, sometimes foul-smelling diarrhea that may alternate with soft, greasy stools, fatigue or malaise, abdominal cramps, bloating, gas or flatulence, nausea, and weight loss."


If you're concerned about the quality of the water in your home, there are a few ways to learn about its safety and whether it contains cysts:

  1. Test the water yourself. Using an at-home kit, you can take a water sample and then mail it to a lab for analysis. An important note: Not all test kits are the same. Make sure the kit you purchase will test for the contaminants you are concerned about.
  2. Request a water quality report. All public water systems in the U.S. are required to provide customers with an annual Consumer Confidence Report that details the water quality in your community, just ask for a copy.
  3. Call the EPA's Safe Drinking Water Hotline for more information about drinking water safety in your area: 1-800-426-4791.


When it comes to cysts, the Environmental Protection Agency says there is no safe or acceptable level of cryptosporidium or giardia in drinking water. The National Primary Drinking Water Regulations (NPDWRs or primary standards) legally enforceable standards that apply to public water systems lists zero as the "maximum contaminant level."


There are two primary ways you can treat drinking water:

  1. Boil it. To kill or inactivate cryptosporidium and giardia, the Center for Disease Control and Prevention (CDC) recommends you "bring your water to a rolling boil for one minute. Water should then be allowed to cool, stored in a clean sanitized container with a tight cover, and refrigerated."
  2. Filter it. The recommended method of treatment is a reverse osmosis system or a point-of-use water filter capable of removing particles less than one micron in diameter.

If you have a well, it's important to test it at least once a year. Annual disinfection is also necessary. Keep in mind; chlorine is not an effective treatment for cryptosporidium and giardia because they are both tolerant of it.


To remove cryptosporidium and giardia cysts, the CDC recommends using filters labeled with any of these four messages:

  • Reverse osmosis (with or without NSF 53 or NSF 58 labeling)
  • Absolute pore size of 1 micron or smaller (with or without NSF 53 or NSF 58 labeling)
  • Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst reduction
  • Tested and certified to NSF/ANSI Standard 53 or NSF/ANSI Standard 58 for cyst removal

These three systems are the top performers:





Regular replacement of the filter and/or cartridge is critical to maintaining their effectiveness and reducing bacterial contamination. An overused or out-of-date filter can become dangerous because the filter will no longer trap contaminants, allowing them to leach back into your water. For the safety of you and your loved ones, it's important not to put off replacement too long. There are four effective ways of knowing when it's time to replace your water filter:

  1. Follow the manufacturer's recommendations. Their specified replacement timing will err on the side of caution so you can be assured that your water quality will always be safe.
  2. Measure usage. Install a filter measurement meter or filter monitor that connects to the incoming water line that feeds the filter system and measures the number of gallons that pass through. Then using the manufacturer's recommended usage limit, program the monitor to alert you when you've reached the allowed number of gallons. You'll know exactly when it's time to replace the filter.
  3. Read your water bill. If your home is supplied with municipal water, your water bill will tell you exactly how much water is used monthly. Compare your actual usage to the manufacturer's recommendation and plan the replacement accordingly.
  4. Monitor manually. If you have non-municipal water, the most cost-effective method is to monitor your filter manually either with your palate or a water testing kit. Start with routine water tests that look for lead, microorganisms and other contaminants to verify whether your filters are still removing them. For drinking water systems, simply fill a glass with water and check the flavor yourself. You'll be able to see or taste when the filter is exhausted and no longer purifying your water because the water flavor will be unpleasant.


For answers to cysts-related questions, recommendations on the best filter for your home or general drinking water questions, contact us.