When it comes to installing a UV water purifier, the best and most efficient placement is after the filter. This is true for both biological filters that have built-in UV light, as well as standalone UV purifiers. It is essential to make sure that the purifier is the last step in the overall filtration setup, as any other filters or water treatment systems installed after it can obstruct the rays from the UV bulb and stop them from reaching all the microbes that pass through the filter. When installing a UV purifier for the first time, it is important to remember that it should always be placed after other filters and water treatment systems. As the water passes through the UV purifier, the microorganisms it contains are exposed to UV light, which eliminates them. To sum up, when installing a UV water purifier, it should always be placed after other filters and water treatment systems in order to guarantee that it is effective in destroying microorganisms.