A liquid filter, particularly for filtering diesel fuel, having a device for automatically discharging water separated from the fuel in the liquid filter, including a housing with an inlet and an outlet for the liquid to be filtered, a filter element arranged in a sealed manner between the inlet and the outlet, and a water collecting area underneath the filter element, in which the automatic water discharge device is connected in a sealed manner to the housing below the water collecting area, and includes in a single housing a sensor for sensing the water level in the water collecting area, an electrically operated water discharge device for discharging water from the water collecting area, a water outlet, and a microprocessor operatively connected to the sensor, to the water discharge device and to a control unit of the internal combustion engine, such that in a predetermined operational state of the internal combustion engine while the engine is running, the microprocessor activates the water discharge device when the sensor emits an appropriate signal indicating water in the collecting area.