This unit replaces the standard 18.93 L (5-gal.) bottles on a water cooler. It uses an internal replaceable filter to purify tap water. Each filter equals 42 water bottles. Apart from being very economical, it means you don't need to exchange heavy water bottles. I am including a new unopened filter. This is a link to the company website: https://www.ghpgroupinc.com/product-details/GWF8.html This is a link to Costco.ca, where filters can be purchased. A three pack of filters costs $79.99 (replaces 126 water bottles): https://www.costco.ca/Vitapur-Replacement-Filters.product.10355119.html Asking $10.00