An eco-village was recently established in Seocheon-gun, Chungcheongnam-do as a part of the garden village promotion business. However, it is thought that the increase in development-caused impermeable surfaces may interfere with the efforts to secure water sources from the surrounding streamlets or maintaining waterways. This study aimed to overcome these problems by applying a rainwater-harvesting system to an ecological housing complex. In this study, rainwater was designed to be used for flushing toilets in restrooms, gardening, or car washing, which resulted in a reduction in the consumption of water and in its outflow. This plan promises an 85% reduction effect in rainwater outflow from rooftops, a 50-ton annual water supply substitution effect per household, and a 1,800-ton water-saving effect per complex.