This guide provides an overview of water-filter products within PATH's Springboard Initiative ecosystem that feature the PATH-developed C1 Common Interface—a common-connection point and platform solution to promote product interchangeability, standardization, and market efficiency. Cartridges from one manufacturer can be used in water filters from another. This guide is primarily intended for professionals who seek balanced, introductory-level information on available water-filter products appropriate for low- and/or lower-middle income consumers in developing countries. It is not comprehensive and covers only products with the C1 Common Interface. The information presented is appropriate for commercial, public-sector, or nonprofit organizations interested in wholesale quantities.