SteriPEN is a hand held water purifier that uses ultraviolet light to purify up to 1 liter (32oz) of water at a time. There are no chemicals to taste or smell, no pumping or test strips, and no setup or clean up involved! The SteriPEN Classic Safe Water System (SP-SYS) is an all-in-one water treatment system that includes the SteriPEN Classic, Water Bottle Pre-Filter and a Nalgene BPA-Free wide-mouth water bottle. This system is all that is needed for treating drinking water while camping, hiking, backpacking or traveling. The 4 micron screen Pre-Filter fits snugly on the wide-mouth water bottle, protecting the drinking threads, and allows clear water to flow into the bottle while removing particulates. See the User's Guide to see how the SteriPEN Classic mates with the Pre-Filter. Ships with neoprene case for the Classic and User's Guide. SteriPEN utilizes C Wavelength UV (ultraviolet light). UV-C light is short wave light, between x-rays and visible light wavelengths, which destroy the DNA of microbes in seconds. Without functional DNA, microbes can't reproduce or make you sick.