From Watershed Process to Human Exposure: A Hydrologic Framework for Water Quality and Environmental Health Investigations

Water quality measurements are essential to environmental health research, but linking watershed observations to human exposure requires accounting for water movement, supply conditions, and use. As monitoring records increasingly inform epidemiological investigations, these distinctions matter for identifying exposed populations and guiding testing, treatment, and source protection. In this critical review, evidence from watershed hydrology, contaminant transport, drinking water research, and exposure science is synthesized to identify where those connections require further investigation. For example, hydrologic connectivity, storage, and biogeochemical transformation influence contaminant delivery, while treatment, distribution, and household practices determine the water people encounter. A Hydrologic Exposure Framework is introduced that links environmental sources and processes, water systems and uses, and human contact. The framework helps distinguish observations from estimates, assumptions, and unknowns for a specified research objective. A hypothetical ingestion example and Appalachian case studies illustrate the different evidence requirements of source attribution and exposure estimation. The framework connects hydrologic process knowledge to measurement decisions that can guide sampling, identify unverified supply assumptions, and clarify interpretation for water users. Future research should evaluate the framework’s effectiveness against other methods to determine where additional pathway evidence improves exposure estimation and source attribution.