Just attach the straw to the filter, place one end in the water and suck through the straw. With a blend of microscopic carbon, binder and antimicrobial particles, the filter will remove more than 99.9 percent of cryptosporidium and Giardia, and even improves the taste of the water. Easy to operate, simply attach the straw to the filter unit, place the filter in the water source and drink through the straw. Note although the filter does reduce bacteria and viruses, it is not certified to remove more than 99.99 percent required by the US EPA water purifier standard. For maximum protection, use in conjunction with water treatment drops or tablets. Comes packaged with two filters and each unit will filter up to 20 gallons.