The KompetenzZentrum Wasser Berlin (KWB) is a private research and development center, created in 2000, with a status of public interest, and mainly supported by Veolia Water and Berliner Wasser Betriebe. This is where I did a six month-training period as part of my studies at the French AgroParisTech ENGREF engineering school. Within the department “Point and non-point source pollution control”, the KWB initiated a program called Aquisafe. The aim is to investigate the mitigation of trace contaminants from diffuse sources in rural and semi-rural areas to improve water quality of surface water bodies. The sustainable way of addressing pollution control is that the selected mitigation metods are natural or nature-based: namely constructed wetlands and riparian1 corridors. To develop knowledge and tools about these mitigation zones, an innovative approach was chosen when conducting the project: - The first part aims at a background study about surface water and pollutions from diffuse sources, leading to a progressive focus on key pollutants for the future of the project. The second part investigates modelling tools as diagnosis tools for the repartition and load of contaminants in a watershed. The third part contains field experiments and uses results from previous parts. The final purpose is to assess the mitigation efficiency of the systems and to optimize their design in the perspective of improving surface water quality. In charge of the first part, I did set the context of the project by reviewing background information on surface waters in Europe and associated pollutions, that move to water via soil surface run-off or subsurface run-off. After using criteria related to the Aquisafe context, the main pollutant families of interest for the rest of the screening process are pesticides used in agriculture, pollutants coming from the spreading of animal waste on land, pollutants coming from the spreading of sludge from wastewater treatment plants, pollutants from natural and extensive areas, and pollutants from transportation networks. During the study it appeared that in a rural or semi-rural area, the land use of the watershed plays a key role in the selection and assessment of priority pollutants coming from diffuse sources and entering surface waters. The importance of this factor should always be kept in mind as the project goes on. The work is still in progress concerning the review of pollutant families, and will lead to the final screening at the molecule level, providing a list of key contaminants for the other parts of the Aquisafe project. Finally the results of Aquisafe will tell if such sustainable mitigation zones can be used as a real innovative management tool of diffuse pollution in a watershed.