A demand initiated method for regenerating a water softener which operates the softener ion exchange bed over a capacity range in which the resin is most efficiently restored by exposure to brine. The reserve capacity of the softener is adjusted in response to the amount of softening capacity used since the last regeneration, as is the quantity of saturated brine to be used for the next regeneration, which is scheduled when the reserve capacity is exceeded, or the remaining available capacity will not be adequate for expected usage on the next day of the week. The method schedules a regeneration when the amount of exchange capacity of the resin bed used since the last regeneration plus the variation of exchange capacity used on the next day plus the average exchange capacity of the resin bed used on the next day is greater than the selected design exchange capacity.