A sterilization system uses an ozone-air mixture for treatment of a water-intake finger and an air space of a water source bottle of a water dispenser in which the bottle is installed with its neck downwards for discharge. The system includes a cone for holding the bottle vertically, the water-intake finger for water delivery from the bottle into a reservoir, an ozone generator, and a control device. Two longitudinal channels in the water-intake finger separately deliver water from the bottle into the reservoir and ozone-air mixture delivery into the bottle. The water-intake finger has a preventive cup, to prevent air penetration into the bottle from the air space of the reservoir, having an inlet channel connected to the generator for ozone-air mixture delivery into the preventive cup during water off-take from the reservoir when water poured out of the bottle is replaced with the ozone-air mixture delivered from the generator.
