In rural areas, small wastewater treatment plants (SWWTP) are a cost-efficient solution to sewage disposal issues. In Europe, small WWTPs are defined as plants for treating domes- tic wastewater up 50 PE. In Germany, about 2.2 million SWWTPs are in operation or are being installed. In France about 10 to 12 million people are served by decentralised sys- tems. There are many different technical solutions on the market, ranging from artificial wetlands, reed bed filters to activated sludge systems. All systems available on the European market have to meet the EU-Certification EN 12566-3, which regulates a minimum standard of op- eration reliability and purification limits. Furthermore, additional guidelines have to be con- sidered, depending on national and regional specifications. There is still a lack of information about performance, operation reliability and maintainability of the different types of SWWTP under real operating conditions. These parameters are however, of particular importance to both customers and service providers. To fill this gap, during a duration time of 14 month in this study 12 different treatment systems were simultaneously compared and evaluated un- der real operating conditions. The study delivers now detailed information about the perfor- mances of different plant models with regard to purification capacity, effluent values, operat- ing expenditures, sludge treatment etc. The results will be published in a user guide. The study was performed at the Training and Demonstration Centre for Decentralised Sew- age Treatment (BDZ) in Leipzig with a special range of small wastewater treatment plant, already installed at BDZ for training purposes as well as two additional plants, which has been installed there especially for the compass study.