Ideal for coffee machines and to reduce scaling.
KDF-GAC filter is a two media cartridge consisting of KDF (Kinetic Degradation Fluxion) and GAC (Granulated Activated Carbon). 
KDF® Process Media are high-purity, granulated copper and zinc-based alloys that treat water through a process based upon the principle of Redox (Oxidation-Reduction).
Basically, KDF creates zinc oxide in the cartridge which helps stop bacteria from growing and allows the carbon to last longer.
 
GAC (granular activated carbon) will remove organic materials VOCs and radon gas by a process called adsorption.
KDF removes metals including lead and hexavalent chromium 6, pesticides, Trihalomethanes THMs, MTBE, and neutralizes chlorine.
KDF combined with coconut shell carbon (GAC or carbon block) extends the life by protecting against bacteria growth.  
 
Most systems use carbon to remove chlorine, but need replacing every 6 to 12 months otherwise bacteria will grow in carbon. But the copper zinc in KDF produces zinc oxide that will inhibit bacteria growth and extends the life of the filter.