A waste water purification plant purifies water by means of plants and a waste water purification process. The waste water purification plant has at least one plant container, a feed unit, an evacuation unit and plants. Waste water to be purified can be supplied to the purification plant by the feed unit. Purified waste water can be discharged from the purification plant by the evacuation unit. The plants are arranged in the plant container without a substrate. A plant container preferably has at least two plant basins. At least one other container can be provided. At least part of the plant container is arranged on the roof of a building. Plants of at least two different plant species are provided in the plant container. Depending on the type of waste water for example industrial and/or sanitary waste water the waste water to be purified may be purified in a predeterminable sequence by the plants of the different plant species. This purification plant makes it possible to purify industrial and/or sanitary waste water, i.e. it is applicable to industries and/or private homes. In particular, the waste water purified by the purification plant should possess a high degree of purity, for example that of drinking water.