Abstract: A visual or audible indicator to indicate the absence of an additive ordinarily added to the rinse or wash water of a commercial dishwashing machine is disclosed. The dishwashing machine includes a separate reservoir containing an additive, a supply line connecting the reservoir to the point within the dishwashing machine where the additive is normally added, and a pump in the supply line for pumping the additive from the reservoir through the supply line. The pump includes a check-valve for retaining the additive in the supply line when the pump is not pumping. The indicator includes a vacuum operated switch and a connecting line connecting the vacuum operated switch to the supply line between the additive reservoir and the pump. The pump, switch, and connecting line are physically located above the maximum possible level of additive within the additive reservoir.