Urban water management plays a crucial role in socio-economic development and each city has its own water demand and water supply patterns. A system dynamics model was then developed to investigate the water demand and supply of Bangkok Metropolitan, Thailand. Influential factors of the water system include economic development, temperature, water conservation programs, waste water treatment, and water infrastructure. Temperature is the main driving force for the water demand, while the pipeline leakage rate is the most impactful factor on the water supply. If no policy intervention is implemented, water deficit will appear in July 2022. The leakage rate at 25% can extend water discrepancy after 2036.