Low Impact Development (LID) practices provide more sustainable solutions than traditional piping and storm ponds in stormwater management. However, architects are not equipped with the knowledge to perform runoff calculations at early design stage. In response to this dilemma, we have developed an open-source stormwater runoff evaluation and management tool, Rainwater+. It is seamlessly integrated into computer-aided design (CAD) software to receive instant estimate on the stormwater runoff volume of architecture and landscape designs. Designers can thereby develop appropriate rainwater management strategies based on local precipitation data, specific standards, site conditions and economic considerations. We employed Rainwater+ to conduct two case studies illustrating the importance of considering stormwater runoff in the early design stage. The first case study showed that integrating rainwater management into design modeling is critical for determining LID practice at any specific site. The second case study demonstrated the need of visualizing runoff flow direction in assisting the placement of LID practices at proper locations when the terrain is of great complexity. (C) 2016 Elsevier Ltd. All rights reserved.