The Impact of Self-assessment on Hydration

The study plans to include firefighters from the Tonto National Forest and the broader Phoenix Valley area, and if needed, other active populations that are similarly active to WLFFs. Participants with high urine concentration (≥1.020 USG) for both samples collected during Part I (screening phase), may be invited to provide an additional urine sample and a blood sample for copeptin analysis during a follow up day (Part II). Participants with elevated USG and copeptin are eligible to participate in the study. Inclusion for PART I is that participants are part of a by the research selected wildland firefighter population (or surrogate population), no further exclusion criteria are followed for PART I. For Part II and Part III the following criteria apply: Inclusion Criteria: * Age 18-65 years * Identifying as male, female or other Exclusion Criteria: * Thyroid medication * Bariatric surgery * Cardiovascular disease * Renal disease * Hepatic disease * Bodyweight \<110 lbs. * Any injury that would not allow physical performance or activity * Pregnant or lactating * Diuretics * Non-stable self-reported body weight for the last month (\<10 lbs. fluctuation) Investigators will not exclude participants reporting the use of dietary supplements as there is no evidence that the accuracy of self-assessment (specifically the accuracy of urine color assessment) to determine a low vs. high urine concentration is influenced by dietary supplement use, but participants will be questioned…