Built specifically for the only EPA registered H2O purifier bottle on the planet, these Exstream Cyst Filters connect to your Virustat cartridge and filter up to 26 gallons depending on the quality of your H2O source. Exstream Cyst Filters remove Giardia and Cryptosporidium from your drinking H2O but eventually require changing to enhance flow and performance. The lightweight design easily fits into any small pouch or pack pocket for convenient travel.