The invention relates to a device (10) for treating a liquid with a plasma, the device (10) having a high-voltage electrode (20) and a liquid-permeable ground electrode device (30). The ground electrode device (30) has a flat, conductive area (32) and a porous area (34) arranged on the flat, conductive area (32), the conductive area (32) being liquid-permeable along its area. A discharge space (40) is formed between the ground electrode device (30) and the high-voltage electrode (20). A first dielectric (50) is arranged on the high-voltage electrode (20), so that a plasma can be generated in the discharge space (40) by means of dielectrically impeded discharge. The device (10) also has a flow volume (60) into which the liquid (12) can be introduced and which is surrounded by a wall (62). The wall (62) of the flow volume (60) has the ground electrode device (30) at least in a first area, so that the flow volume (60) is connected to the discharge space (40) via the ground electrode device (30) in a liquid-permeable manner.