As a typical megacity facing water quality-induced water scarcity, Shanghai suffers from limited local water resources. Although transit water resources are abundant, the security of its water supply is severely challenged by threats such as saltwater intrusion and sudden pollution incidents. Based on the natural geographic conditions and water resources zoning of Shanghai, this paper introduces the composition of the city’s water resources, the characteristics of water quantity and quality, and the current utilization status. Based on existing research, methods for analyzing and estimating local water resources, transit water resources and their corresponding exploitable quantities are summarized. The limitations of certain traditional methods when applied to highly urbanized river network regions are identified and future research directions are proposed.