To strive to full self-sufficiency in water, Singapore has invested heavily in desalination, wastewater reclamation (branded as NEWater), water catchment management and other similar projects. Among the many alternatives to augment Singapore's water supply, decision-makers need to know which one is the most sustainable plan to pursue. This research project aims to demonstrate the usefulness of System Dynamics (SD) as a decision support tool to help achieve sustainable water management in Singapore. We have developed a system dynamics model called SingaporeWater and analyzed the long-term impacts of various investment plans. We discovered that investing in underground water storage or surface water catchments alone is not sufficient to help achieve self-sufficiency in water. If Singapore starts to invest in desalination or NEWater only after there is inadequacy of water, then it will result in about five years of water shortage followed by another five years of water abundance. The results highlight the need to build water infrastructures well in advance in order to meet Singapore's future water demand.