Simplex systems are equipped with one ion exchange column, duplex systems with two such columns. The main advantage of duplex systems with several columns is that no breaks in operation are necessary and the columns can alternate. This means that more fresh pearl water is available at all times.
In simplex systems with only one column, pauses must be taken for regeneration. However, most of the units are programmed to do this automatically at night, when little water is needed and there is still a reservoir of treated water.