APEC Water PHPLUSKIT-38 is a perfect add on kit to compliment any existing or new RO drinking water systems. The 10" inline alkaline mineral cartridge adds only 100% US-made food-grade calcium carbonate to effectively neutralize acidity, raise pH in the water, and enhance water taste for people who prefer mineral water. Other re-mineralization filters claim to add various beneficial minerals back into the water; however, their mineral formulations are often from unknown sources that can lead to a potential health concern. This premium pH filter provides only the simple and essential alkaline water without any additives added to ensure your health. The kit is compatible with most standard RO systems with 3/8 in. output.