New. A Backpacker Magazine 2016 Editors' Choice winner, the MSR Guardian Purifier physically removes viruses, bacteria, protozoa and dirt quickly and easily on backpacking trips and international travel. Features Winner of both Backpacker Magazine's 2016 Editors' Choice Award and Outside Magazine's 2016 Gear of the Show Award Unlike conventional hollow-fiber technology, the advanced medical-grade fibers in the Guardian block viruses—something most other hollow-fiber filters cannot do. Physically removes viruses, bacteria, protozoa and particulate, including hepatitis A, E. coli, giardia, cryptosporidium and more. Purifies 2.5 liters per min. With every stroke, the purifier uses 10% of its water to flush the contaminants in its filter back into the source; this means you'll never have to hassle with back-flushing. Rugged construction is designed to withstand freezing and drops up to 6 ft.