This filter is a in-line filter for the Stainless Steel Counter-Top Water Filtration unit (sku #SS-CT-WF & Sku #SS-CT-WU).
You simply install this filter in-line between the sink and your countertop water filter and you hhave added an extra level of water filter purification.
In areas that have heavy sediment and dirt in the water we recommend using the optional Pre-Filter in order to enhance the life of the filter cartridge.