The Aquatic Life Twist-In 100 GPD 4-Stage Reverse Osmosis Osmosis Deionization (RODI) filtration system is a very compact water purification solutions that efficiently combine reverse osmosis RO technology with their quick and easy to change twist-in replacement filter cartridges. The new twist-in media cartridge design makes filter changes simple, easy and clean – no tools required and no mess! The twist-in cartridges can be easily changed in only seconds with just a quarter turn and without contact with used filter material, and the supply water to the unit does not have to be turned off to replace any cartridge.