First, the raw water enters a 25 micron prefilter cartridge to remove the heavy sediment. Then, the raw water enters the distribution tube and travels through the distribution basket. These form a maze of torturous paths through which the water flows. The filtered water then exits the unit and passes through a 5 micron post-filter which catches any carbon fines that might leave the unit upon initial flush. The water is then ready to use.
Water chemistry is different throughout the world.
This water has been run through the filter until any one of the contaminants was no longer removed in sufficient quantity to meet EPA limits. At that point, the test was stopped and the gallonage noted. That gallonage is the compliance capacity of the units. These systems are also certified to the requirements of some states. Shower in chlorine-free water.