two different filter combinations have been tested as candidate systems for bypassing the reverse osmosis membranes of the army's rowpu when treating fresh water: a spiral-wound cotton prefilter of 5.0 micrometers nominal pore size combined with either a melt-blown polypropylene depth filter or a pleated polypropylene filter of 3.0 micrometers absolute pore size. test organisms were klebsiella terrigena, cryptosporidium parvum oocysts, rhodotorula rubra, and 3.7 micrometers latex beads. challenge waters were dechlorinated tap water and a worst-case water containing ac fine test dust and humic acid. the depth filter, tested separately, achieved better than 99.9 percent reduction of c. parvum oocysts (the usepa criterion) at filtration rates of 1-2 gpm under all conditions. the pleated filter did not achieve 99.9 percent reduction of c. parvum oocysts at a filtration rate of 1 gpm. none of the filter combinations tested was adequate for the removal of k. terrigena.... filtration, bacteria, cartridge filters, water supply, protozoan cysts