A polishing cartridge in a water purification system for final purification of water for distribution to a point of use. The system includes a closed water recirculation loop supplied at one point by a water inlet with water to be purified, and having at least one outlet point of use of the purified water, a pump and a water purifier on the loop respectively downstream of the inlet point and upstream of the at least one outlet point, in the water flow direction, and two independent valves on the loop. The system further including a hydraulic connector including four ports that forms a distributor or manifold for the system. The cartridge contains a combination of an ultra filter having a cut-off below 13000 daltons for reducing the level of pyrogens and nucleases contained in the water, and C18 grafted media effective for reducing the level of contaminants in the water.