The invention relates to a device (10) for treating a liquid with a plasma, wherein the device (10) has a high-voltage electrode (20) as well as a liquid-permeable ground electrode device (30). The ground electrode device (30) has a flat, conductive region (32) and a porous region (34) arranged on the flat, conductive region (32), wherein the conductive region (32) is liquid-permeable along its flat extension. 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 a dielectric barrier discharge. Moreover, the device (10) has an initial flow volume (60) into which the liquid (12) can be conducted, and that is surrounded by a wall (62). At least in a first region, the wall (62) of the initial flow volume (60) has the ground electrode device (30) such that the initial flow volume (60) is connected to the discharge space (40) in a liquid permeable manner via the ground electrode device (30).