For starters, what is Cryptosporidium?
Cryptosporidium is a microscopic parasite that lives in the intestine of infected animals and humans. It passes in the stool in its dormant oocyst form. The oocyst is protected by an outer shell that allows it to survive outside the body for long periods of time and makes it very resistant to chlorine-based disinfectants. It occurs mainly in surface water sources, such as lakes, streams, and rivers. In healthy adults, Cryptosporidium can cause illness, but for people with weakened immune systems, it can cause severe illness and even death.
Those who wish to take extra measures to avoid waterborne cryptosporidiosis can bring their drinking water to a boil for a full minute. Boiling water is the most effective way of killing Cryptosporidium. As an alternative to boiling water, people may take the following measures:
Use a point-of-use filter: Consider using point-of-use (personal use, end-of-tap, under sink) filters that remove particles one micrometer or less in diameter. Filters that use reverse osmosis, those labeled as “absolute one-micron filters,” or those labeled as certified by an American National Standards Institute (ANSI) - accredited organization to ANSI/NSF Standard 53 for “Cyst Removal” provide the greatest assurance of removing Cryptosporidium. As with all filters, follow the manufacturer’s instructions for filter use and replacement.
Use bottled water: Check the label or call the bottler to find out how bottled water is treated.
The following bottled water treatments protect against Cryptosporidium: reverse osmosis, distillation, ultraviolet light, or filtration with an absolute one-micron filter. Bottled waters derived from protected well and spring water sources are less likely to be contaminated by Cryptosporidium than those containing untreated municipal drinking water from less protected sources such as rivers and lakes. Those who choose to take these precautions should remember that they can be exposed to waterborne pathogens through water used for brushing teeth, making ice cubes, and washing fruits and vegetables – not just through the water they drink.
There are several other treatment options to help protect your home from cryptosporidiosis. Distillation units, reverse osmosis, and filters with an "absolute" rating of 1.0 micron (sometimes called 1.0 micrometer) or those labeled as certified by NSF International as meeting NSF Standard 53 for Cyst Removal provide the greatest assurance of removing the germs that cause cryptosporidiosis.
There is one caution to this terminology: the "nominal" one micron (micrometer) rating is not standardized, and many filters in this category may not remove the germs that cause cryptosporidiosis. An "absolute" 1.0-micron rating means that none of the openings in the filters are bigger than 1.0 micron, in contrast to a "nominal" one-micron rating, which means that most of the openings are 1.0 micron in size but that some are smaller and some are bigger. It is these bigger openings that may let some of the germs through.