Natural purification systems have already been used for years in The Netherlands to improve the quality of waste water before discharge or reuse. The first basic ideas design for the ‘Waterharmonica’ as the link between the Water Chain and the Water System were rewarded by the Foundation for Applied Water Research (STOWA) on its 25th anniversary in 1996. Since then, Waterharmonicas have been constructed in various places in The Netherlands, firstly on a small scale but now also on a large scale. Extensive research has been carried out into the working and effectiveness of these systems over the past 15 years and they are still being studied. Moreover, the Waterharmonica became rooted in Dutch water policy (Uijterlinde, 2012). The picture with regard to the applications of, and research into, Waterharmonicas is summarised and discussed in this report.