Abstract: A device for the dosable addition of accurate quantities of liquid disinfecting agent to water, having a reservoir for the water, and a supply container for the disinfectant. A dosing pump feeds the disinfectant in regulatable amounts from supply container to the water flowing from the reservoir. In order to reduce constructional costs and to increase the dosing accuracy, the water reservoir has a liquid level-control device and an outlet line. The quantity of the outflowing water is controlled accurately solely by the existing static pressure of the water level in the reservoir. The fluctuation in dosing is less than 2%.