A water budget is a balance sheet of water inflows, outflows, and storage changes within a specific system, such as a watershed, aquifer, or lake. The water budget is significant in hydrology and water resource management for understanding the availability of water resources, managing water supply, and assessing the impacts of land use and climate change on water systems.
Reference: Viessman, W., & Lewis, G. L. (2003). “Introduction to Hydrology.” Prentice Hall.