The two tank (one resin tank and one brine tank) models are designed for water supplies where consumption of daily water usage is not highly erratic and water is not consumed during certain hours of the day. This would include households. These models can be set to regenerate during hours of non-use, which is normally during the night. These units can also be used for small businesses that have normal business hours. These models are sized so that there will be several days water consumption before a regeneration is needed. This is to provide an ample reserve in the event of unexpected water usage.