Abstract: A device supplies water into a high-pressure fuel pump of a motor vehicle internal combustion engine, wherein the water is admixed to the fuel in the inlet region of the high-pressure fuel pump in a controlled manner by a metering valve, and wherein the device is designed to guide the water at least from a part of a supply line back to the storage container. When viewed in the flow direction from the storage container to the high-pressure fuel pump, a shut-off valve is provided in the supply line upstream of the metering valve, and the supply line is designed to elastically deformably change its volume in a line section positioned between the valves.