This two-package (H2 ultra water replacement) of AlkaViva water ionizer filters conveniently includes both the Prefilter + UltraWater filter for your H2 Series ionizer. This is the BEST filtration system that you can buy. (Each hydrogen rich water ionizer filter rated for 3785 L/1000 Gallons and replaces at the same time). The Prefilter always goes on the RIGHT side as you are facing your ionizer.