The primary usage for a UV light is to disinfect filtered water at a certain flow rate. Bacteria, viruses, and other microorganisms are destroyed by the UV interfering with the DNA and RNA in the organisms' reproductive cycles. In theory, the reverse osmosis membrane already removes bacteria and viruses from the water, therefore, if you are on a municipal water system (tap water) in the U.S., chances are that you should not need a UV light on top of our ULTIMATE RO System. But, if your water source is known to be unsafe with microorganisms and you want to have extra protection, then you can add an UV as an additional stage to disinfect water.
Note: The UV light When is purchased together with an APEC RO system, it will come already installed for you. Also this ultra violet light can be added on to any existing RO system.