A method and a device for open- or closed-loop control of an amount of water mixed with a fuel is provided. A fuel supply is split into a first branch having a Venturi pipe with a vacuum connection and a second branch having a blocking valve. Water is supplied to the Venturi pipe vacuum connection, and the fuel-water mixture in the first branch and the fuel in the second branch is supplied to the fuel pump. Open-loop or closed-loop control is provided by either reducing fuel flow in the second branch with the stop valve such that the fuel flow in the first branch increases, increasing the amount of water mixed in the fuel at the Venturi pipe, or increasing fuel flow in the second branch such that first branch fuel flow decreases, decreasing the amount of water mixed in the fuel at the Venturi pipe.