Dr. Paul Auerbach is the world's leading outdoor health expert. His blog offers tips on outdoor safety and advice on how to handle wilderness emergencies.
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Sawyer Products, Inc. has released a new hollow fiber membrane water microfilter that will filter out bacteria, protozoa, and viruses, because it filters out particles down to the 0.2 micron size. It is rated to perform for up to 3,000 gallons before the filtration unit should be replaced, and can handle a pressure of up to 40 pounds per square inch (PSI). This product (Sawyer® Water Purifier) comes packaged with a polycarbonate bottle and faucet adapter. A water bag for attachment may be purchased. Upon request, the company will provide literature that describes a virus removal test of the Sawyer®7/6BV filter, which is incorporated into the unit.
Another product (Sawyer® Water Filter) has a larger-pored filter, so is recommended for bacteria and protozoa, but not for viruses. It is rated to perform for up to 500 gallons. They both have reasonable flow rates, so that arduous pumping is not necessary to achieve reasonable volumes of filtered water in a brief period of time.
Cost estimates based upon useful filter life and retail cost of the filters indicates that the Water Filter achieves filtration at a cost of 7 cents per gallon, and the Water Purifier achieves filtration at a cost of 4 cents per gallon. Both filters can have their effective lives extended by filtering “pre-filtered” water (which has had large particulates removed), filtering water that has “settled” in order to isolate less contaminated water, and pulling water from below the surface of a fresh water body, but not from sediment-laden bottom water.
As for many other products on the outdoor retail market, the consumer must rely upon manufacturer’s claims and literature from independent testing agencies to have confidence in the capabilities of the products.
