nuvoH2O Studio Complete Salt-Free Water Softening System - Old 2012 Model Water flow: 12-15 gpm with 3/4-Inch ports (no change to existing flow) Capacity: about 25,000 gallons (average annual water usage of household of 2) Uses 10-Inch Salt-Free Replacement Cartridges, Eliminates existing damaging scale other products may prevent scale buildup but dont remove existing scale, No harmful salt avoid the hassle of constant salt replenishment and protect your health and our environment from the harmful effects of salt used in other softeners.