A water-steam circuit of a power plant includes at least one low-pressure steam system and a reservoir for waste water from the water-steam circuit, wherein the reservoir has, in addition to at least one waste water feed line, a further heat supply from the water-steam circuit and a steam outlet which is connected via a waste steam pipe to the low-pressure steam system of the water-steam circuit. A method for cleaning waste water from a power plant having a water-steam circuit, wherein the waste water is conducted into a reservoir and, in addition to a steam fraction generated by automatic evaporation of waste water in the reservoir, a water fraction that is also produced is evaporated using energy from the water-steam circuit, and the entire steam mass flow is introduced into a low-pressure steam system of the power plant.