A grate (111)-covered gutter (110) of a paved part of the earth's surface (100) is temporarily closed off by means of a closing organ (130), the gutter (110) being connected to a sewage pipe (120). Thus, the draining away of contaminating liquid can be prevented. The closing organ (130) includes a valve (131 fitted rotatably in the gutter (110). The valve (131) can be in a first stable position wherein the valve (131) seals. The valve can also be in a second stable position in which the valve (131) releases the gutter (110) for the discharge of liquid (rainwater) to the sewage pipe.