Ultrafiltration (UF) is similar to reverse osmosis, in that pressure is used to force water molecules through a porous membrane. However, the pores of a UF membrane are about 10 times larger in diameter than the pores of an RO membrane.

Because of this, the driving pressure can be much lower (25-50 psi), and any dissolved solids in the water will pass right through the membrane. The UF membrane removes suspended solids, colloids, bacteria, pyrogen, endotoxin, DNase and RNase from the water. In a laboratory water purification system, the ultrafilter is used to remove pyrogen, endotoxin, DNase and RNase.