● Nanofiltration and reverse osmosis: The pore size is smaller, usually below 0.001 microns, and can completely remove most microorganisms and viruses including E. coli. It is one of the most effective water treatment technologies at present.

Filtration is a method of separation using filter media. Filters are typically able to remove particles as small as about 1 micron, but are unable to remove some dissolved chemicals. Ultrafiltration is a filtration method based on hollow fiber membranes. Ultrafiltration membranes have very tiny pore sizes, usually between 0.01 and 0.1 microns, and are able to filter out even smaller particles and microorganisms, and even viruses and most bacteria.