For use with the Platypus Gravity Works Water Filtration System that treats 4 liters in less than 2.5 minutes without a single pump or stroke. Unfiltered water goes into one reservoir and comes out filtered in the other reservoir. Fill the unfiltered reservoir as needed to have a constant reserve of drinking water. Quick-disconnect fitting allows for easy removal. Cartridge filters 1,500 liters. Made in USA.