“Hard water” has a high mineral content, largely made up of calcium and magnesium carbonates. If your faucet or sink shows sign of limescale, it means that you have hard water in your area; Ion Exchange resin is a common water softening agent and remove excess calcium and magnesium from your water. Ensuring great drinking water for your pet and prevents limescale build-up affecting the performance of the water pump; Each filter includes: 1) Sponge filters the water from food, hair & debris; 2) Activated carbon absorbs bad taste, odor & other chemicals from our tap water. 3) Ion-Exchange resin softens water (removes calcium & magnesium);We recommend to change water softening filter pad monthly; Water Softening Filter Pads works in all Cat H2O and Dog H2O fountains to soften your pet's drinking water.