While reverse osmosis does do an excellent job of removing bacteria and other biological matter, one should not rely upon it as their sole bacteria removal system — especially when treating raw water from the environment — because particularly small biological matter can occasionally slip through the pores of the RO filter.
If bacteria or other biological material exists in the source water, many drinking water professionals suggest using an ultraviolet water sterilizer system in conjunction with a reverse osmosis water filter. The UV water system effectively kills and/or sterilizes biological contaminants.
Looking for a less expensive alternative to ultraviolet water sterilizer systems?
Ultrafiltration Membrane Capsule is an inline UF membrane that is used to prevent bacteria contamination in Reverse Osmosis tanks and other places where a small inline filter is needed to prevent bacteria from entering water lines or containers.
Ultrafiltration (UF) is an important purification technology used for the production of high-purity water. UF is effective for the removal of colloids, proteins, bacteria, viruses, parasites protozoa and pyrogens, (e.g., gram-negative bacterial endotoxins), and other organic molecules larger than 0.01 Micron size and most other water contaminations known today.
Also removes pesticides and herbicides, as well as the hardness in water and salts. ( source )