While head and neck cancer (HNC) is highly curable, primary radiation treatment (RT) is nonetheless challenging. Despite intensive, high-quality, multidisciplinary symptom management of HNC patients during RT, up to 80% of these patients experience moderate to severe levels of oral mucositis making it nearly impossible to drink sufficient fluids and necessitating opioid care for pain. Our data show that 27 - 32% of HNC patients are admitted to inpatient or emergency room (ER) units during RT. Those admissions related to dehydration (and the accompanying costs) are largely preventable, provided at-risk patients can be identified early for intravenous fluid rehydration. Currently, given standard of care for HNC patients undergoing RT, clinicians assess patients only once per week during standard clinic visits. However, the physiological changes underlying the onset of dehydration can develop rapidly, often between clinic visits. In the proposed project, we focus on this missed opportunity for prevention by testing the efficacy of a novel method for home-based dehydration assessment and early intervention to reduce dehydration risk.