CDC guide to water filters

The link to the information below was lifted from a PCT blog site:

A Guide to Water Filters
Filtering tap water: Many but not all available home water filters remove Cryptosporidium. Some filter designs are more suitable for removal of Cryptosporidium than others. Filters that have the words "reverse osmosis" on the label protect against Cryptosporidium. Some other types of filters that function by micro-straining also work. Look for a filter that has a pore size of 1 micron or less. This will remove microbes 1 micron or greater in diameter (Cryptosporidium, Giardia). There are two types of these filters — "absolute 1 micron" filters and "nominal 1 micron" filters but not all filters that are supposed to remove objects 1 micron or larger from water are the same. 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 (like Cryptosporidium) to pass through.

NSF-International (NSF) does independent testing of filters 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 48113 USA, toll free 800-673-8010 or 888-99-SAFER, fax 734-769-0109, 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 filters 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, including filters with reverse osmosis and those that have an absolute pore size of 1 micron or smaller.

Package and Label Information for Purchasing Water Filters
Filters designed to remove Crypto
(any of the four messages below on a package label indicate that the filter should be able to remove Crypto)
Reverse osmosis (with or without NSF testing)
Absolute pore size of 1 micron or smaller (with or without NSF testing)
Tested and certified by NSF Standard 53 or NSF Standard 58 for cyst removal
Tested and certified by NSF Standard 53 or NSF Standard 58 for cyst reduction
Filters labeled only with these words may NOT be designed to remove Crypto
Nominal pore size of 1 micron or smaller
One micron filter
Effective against Giardia
Effective against parasites
Carbon filter
Water purifier
EPA approved Caution: EPA does not approve or test filters
EPA registered Caution: EPA does not register filters based on their ability to remove Cryptosporidium
Activated carbon
Removes chlorine
Ultraviolet light
Pentiodide resins
Water softener
Chlorinated

Note:
Filters collect germs from water, so someone who is not immunocompromised 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.



http://www.cdc.gov/crypto/gen_info/filters.html