A water purifier for supplying high purity water with a low total organic carbon content. The purifier includes removable cartridges that contain a series of organic and ion exchange purification media. Special couplings are used to permit the cartridges to be easily and quickly connected to and removed from the water purifier. In addition, the cartridges contain a check valve to minimize water drainage from the cartridge when the cartridge is removed. Selected water purifier components are constructed of fluorinated polyethylene.