The treatment of rainwater is typically performed by the diversion of the first flush and the use of strainers to retain gross particles (e.g. leaves). To date, there is a lack of rainwater treatment systems with both high efficiency to remove small suspended particles, and simple operation without energy consumption and associated greenhouse gas emissions. The objective of this work was to develop and test a novel concept for the filtration of particles in raw rainwater with no energy usage, self-cleaning mechanism, and simple installation and operation in buildings. For this purpose, an innovative concept was developed based on an up-flow filtration with down-flow backwashing operation. The concept was tested by building a prototype, in which the treatment efficiency for particle removal as well as the backwash efficiency were assessed for three different filter media. Results showed that the system designed under the proposed concept operated effectively with the correct selection of the filter medium. Therefore, the proposed rainwater treatment concept offers an opportunity to enhance water security by treating and using rainwater in buildings in an efficient, simple, and energy-free way. (C) 2013 Elsevier B.V. All rights reserved.