Arches Watercolor Book 10X7 Leak-proof technology for perfect fit without water leaks. Retains the beneficial minerals in water for better health. Remove over 99% of numerous potentially harmful contaminants, using a high grade carbon block. It is recommended to replace the filter every 6 months or 300 gallons, whichever comes first. Premium carbon block used in our filters is made of selected coconut shell. The porous structure offers a high contaminant-adsorption rate.