Belgium is amongst the small European countries. It is a federal state. divided into three regions, corresponding to two different communities (walloon region and Flanders) and a special Region status for the shared head city (Brussels). Water management belongs to the Regions. The water Directive voted by the European Parliament has been transcribed into Belgian legislation and has to be applied by Regions. The legislation requires that any produced wastewater has to be treated adequately before discharge into environment. This paper will deal neither with industrial, nor agricultural applications of the law, but will focus on the domestic wastewater production, its problems and onsite implemented treatment solutionsl. 12% of the walloon population( inhabitants of small villages in rural areas) will never be connected to any sewage network and thus to any treatment station, such as for cities. Before the end of 2015, these people must treat their own wastewater with officially recognized or not treatment systems. A method has been developed by the Agricultural University of Gembloux as a decision supporting tool for individual or collective systems. The software, named SAIWE (Système d'Assistance et d'lnformation Wallon pour I'Epuration autonome) is a step by step analysism methodology aimed at helping deciderst o identify technical solutions (treatment plants) and to irnplemenl the best suited to local constraints. his paper summarizes official guidelines for those onsite solutions, and gives an overview of natural wastewater treatments applied in Belgium, especially with constructed wetlands use.