We still have to deal with a big amount of undesirable waste water effluents in our present society. Municipal, agricultural and industrial waste waters are examples of point source pollution of the surface water. Even the effluent of a Waste water Treatment Plant (WTP) can be a point source of pollution, despite the fact that the quality of the water normally reaches the quality standards. According to the European Water Framework Directive, the quality of the surface water and ground water in Europe has to reach a high standard (good ecological status) by the year of 2015. According to the European Commission point source pollution is one of the most important problems of the diminishment of water ecosystems (http://ec.europa.eu/environment/water). So there is a big pressure to deal with this type of contamination. Within the last years, there is more and more interest for the use of helophytes in constructed wetlands. Several systems are already in practice. Their performance is different and much depended on the conditions and eco-hydrological processes. Most of the time the performance of a constructed wetland is measured by considering it as a black box system, without investigating the processes which take place in the wetlands. There is need for more integrated studies of plant systems to optimize them. In this survey I focus on constructed floating treatment wetlands. Here the sewage water flows through a water basin where constructed mats carry helophytes, which roots hang in the water.