Ultrafiltration (UF) is a filtration process which uses a membrane to force water through a semi-permeable membrane using hydrostatic pressure. This process provides water having low silt density and high purity by filtering out bacteria, viruses, pathogens, endotoxins, suspended solids present in it.

In this process, the solutes having more molecular weight and suspended solids are filtered out and the water along with less molecular weight solutes passes through the semi-permeable membrane. Ultrafiltration process is similar to Reverse Osmosis and Micro-Filtration; it only differs in the size of the molecule which it separates out.

Ultra-filtration process is used to remove the colloidal particles from water whose size ranges from 0.01 to 1.0 microns along with some largely dissolved impurities. The removal of size and type of the contaminants depends upon the pore size of the UF membrane. The pore size in the membrane ranges from 0.005 to 0.1 micron. A measurement roughly used is known as Specific Molecular Weight Cutoff (MWC) which denotes the size of the contaminants removed by a specific UF membrane.