How is a "Filter" Different from a "Purifier"
A water "filter" generally claims to reduce or eliminate only protozoan parasites and bacteria. A filter is adequate for remote wilderness seldom visited by people.
A water "purifier" also removes or inactivates viruses and is therefore ideal in any situation.
The U.S. Environmental Protection Agency (USEPA) regulates and registers microbiological water purifiers because they make pesticidal claims. A purifier must pass the USEPA Test Protocol for Microbiological Water Purifiers, demonstrating that it eliminates 99.9% of protozoan cysts, 99.9999% of waterborne bacteria, and 99.99% of waterborne viruses.
Courtesy of Cascade Designs