Every Drop Counts: Water Balance in Orange County, California & Its Implications On Integrated Water Management

North Orange County, California, is a semi-arid area with limited natural water resources and complex water infrastructure to meet its increasing water demand. The area relies heavily on imported water despite its preeminent wastewater reuse and groundwater replenishment system. Local sources of runoff are challenging to capture and use as water supply. Winter storms are often flashy (short duration) with much of the wet weather runoff lost quickly to the ocean, and dry weather nuisance urban runoff poses water quality challenges. Both dry and wet weather urban runoff is regulated by Municipal Separate Storm Sewer System (MS4) permits. To expand the water portfolio and to meet increasing water quality requirements, OC Public Works has begun collaborating with water and wastewater agencies in the area through the Watershed Improvement Projects Subcommittee to identify and prioritize multi-benefit integrated water project opportunities in collaboration with a wide array of watershed stakeholders. As part of its watershed project planning efforts, a regional water balance evaluation has been developed that includes stormwater, imported water, wastewater, dry weather urban runoff, water recycling, and other sources to provide a holistic understanding of the sources, sinks, transformation, and movement of North Orange County’s diverse water resources. It also provides a tool to identify the critical processes and categories for water quality and water resources management. This water balance will be a useful tool to assist the integrated regional water planning to achieve the most efficient and cost-effective results in both water resource and water quality.