Frequent inundation has become a serious problem in urban areas. It is necessary to improve rainwater retention/infiltration in the urban watershed. The purpose of this study is to report how private rainwater-retention/harvesting facilities can be spread gradually but steadily in the city by citizen initiated activities. Rainwater harvesting tanks were installed intensively and a rainwater harvesting house was constructed in the city of Fukuoka, Japan after the city experienced a flood disaster. The former enhanced users' daily preparedness for emergency, and the latter inspired construction of a rainwater harvesting housing complex. A public elementary school is in use from April 2016, which is inspired by these facilities. The school premises are located on the land reclaimed from an old irrigation pond. Thus the school needs to be adapted to this condition. 3000 m(3) of rainwater can be retained within the premises. The amounts of retention and discharge are monitored, and the data is utilized for science education. In big cities, people tend to depend too much on the top-down, mega-system, which invites more impervious surfaces in urban areas. Bottom-up, individual/collaborative approaches should be adopted in order to achieve multiple purposes of preventing/mitigating disasters, preserving/conserving ecosystems and nurturing/rebuilding communities in the city. (C) 2016 Elsevier Ltd. All rights reserved.