Removing Cryptosporidium : A guide to filtered drinking water

Many, but not all available filtered drinking water systems remove Cryptosporidium. Some filter designs are more suitable for removal of Cryptosporidium than others.

Why is it so important to remove Cryptosporidium ?

Cryptosporidium is a protozoan parasite affecting the gastrointestinal tract of humans and animals. It is shed in the feces in the form of an “oocyst,” which has a hard shell to protect it from the environment. Infections may be asymptomatic or may cause watery diarrhea and abdominal cramps. The organism is transmitted by the fecal-oral route. Outbreaks have most commonly been associated with person-to person (day care center) and waterborne (drinking and recreational water) modes of spread. Foodborne and animal-(especially calves) to-person spread has also been documented.

Filtered drinking water systems that have the words "reverse osmosis" on the label protect against Cryptosporidium. Many other types of filters that work by micro-straining also work. Look for a filter that will remove particles that are less than or equal to 1 micron in diameter. There are two types of these : "absolute 1 micron" filters and "nominal 1 micron" filters. The absolute 1 micron filter will more consistently remove Cryptosporidium than a nominal filter. Some nominal 1 micron filters will allow 20% to 30% of 1 micron particles to pass through.

NSF-International (NSF) does independent testing of filtered drinking water systems to determine if they remove Cryptosporidium. To find out if a particular filter is certified to remove Cryptosporidium, you can look for the NSF trademark plus the words "cyst reduction" or "cyst removal" on the product label information. You can also contact the NSF at 789 N. Dixboro Road, Ann Arbor, MI 48105 USA, toll free1-877-867-3435, fax 313-769-0109, email info@nsf.org, or visit their Web site at www.nsf.org/certified/DWTU/. At their Web site, you can enter the model number of the unit you intend to buy to see if it is on their certified list, or you can look under the section entitled "Reduction claims for drinking water treatment units - Health Effects" and check the box in front of the words "Cyst Reduction." This will display a list of filters tested for their ability to remove Cryptosporidium.

Because NSF testing is expensive and voluntary, some filtered drinking water systems that may work against Cryptosporidium have not been NSF-tested. If you chose to use a product not NSF-certified, select those technologies more likely to reduce Cryptosporidium, this includes filters with reverse osmosis and those that have an absolute pore size of 1 micron or smaller.

Filtered drinking water systems collect germs from water, so someone who is not HIV infected or immune impaired should change the filter cartridges. Anyone changing the cartridges should wear gloves and wash hands afterwards. Filters may not remove Cryptosporidium as well as boiling does because even good brands of filters may sometimes have manufacturing flaws that allow small numbers of Cryptosporidium to get in past the filter. Selection of NSF-Certified filters provides additional assurance against such flaws. Also, poor filter maintenance or failure to replace the filter cartridges as recommended by the manufacturer can cause a filter to fail.

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