Water demand is increasing because of population increases and industry developments as well as demands for improved living standards. Existing water treatment and supply systems cover large areas and have a centralized system; consequently, development of new water resources requires a construction of pipe infrastructure over long distances. The variability of water quantity, as climate changes, is hampering efforts to secure water resources and decide facility capacity. Therefore, a new urban water management system to address these problems is required. This study suggests such a system as well as a new index, i.e., the water self-sufficiency ratio (WSSR) for evaluating the system. WSSR is calculated by dividing the total self-provided water quantity with the total water use in a city. The current WSSR for Suwon City is 11 %, but there are plans to achieve 50 %. This would be accomplished by using rainwater (26.8 million ton/year), encouraging water conservation (31.3 million ton/year), building tunnel-type rainwater-retention facilities (2.5 million ton/year) and reusing treated sewage (1.72 million ton/year). In addition, financial incentives are expected through such as reduction of floor area proportion, tax reduction and governmental subsidies. The WSSR is expected to be useful in evaluating urban water self-reliance as well as in quantitativly establishing a sustainable water management system.