The studies objective is to assess the efficacy of hydration education and the use of a self-assessment worksheet vs. a no-intervention control on improving fluid intake and hydration status in underhydrated wildland firefighters (WLFFs) and their surrogates.

Part I allows to understand hydration status of the participants (screening phase), Part II confirms if participants indeed are deemed to be low fluid consumers, and Part III of this research is a clinical trial that will focus on the optimization of hydration by improving fluid intake (and as a result lowering urine concentration) allowing participants theoretically to improve exercise performance (acute) and optimize health on the long term.

Enrollment will take place until enough people have been screened and be eligible to be enrolled in PART III of the study.

Aside from allowing the investigators to better understand the hydration status of participants in PART I, this part will help to determine potentially eligible participants that can be confirmed through PART II by collecting again a urine sample, and if again concentrated urine is confirmed the research team will take a 5 mL venous blood draw performed by a trained phlebotomist to confirm elevated a copeptin level. These confirmed participants can then be enrolled in PART III of the study when eligible.

PART I includes all participants:

Two urine samples and questionnaire at one day. Expected duration of 2-3 minutes per urine sample and 2-3 minutes for the participant demographics questionnaire which will also be used as a screener to identify eligibility for PART II and III.

PART II includes a smaller sample:

Collection of a urine sample and a blood sample at one follow up day for the duration of 10 minutes.

PART III, the intervention study (being a clinical trial):

Includes n=38 participants, that will invest a maximum of 2 hours and 15 minutes as part of the data collection over a period of 6 days, which includes:

• Education session (pre: INT, or post: CON) of 25 minutes.
• Consuming labelled water and providing a urine sample and bodyweight the day before the start of the study, 10-15 minutes.
• Participate in the study for 6 days (during normal work days) and bodyweight will be measured at day 2, 4 and 6 of the study, during all study days both INT and CON will provide a morning urine sample (and if possible an afternoon/evening sample after work), and during each days sensors will be attached to participants upper arm and gear, 5 minutes per day, 25-30 minutes total.
• The intervention group will track its use of the tools we have provided them with, while the other group will not perform any additional self-assessments during the study period, 10 minutes per day 25-50 minutes total.
• Final hydration strategy questionnaire for INT and CON, 5-10 minutes.

Allocation to INT or CON depends on the total number of participants at different locations that will be eligible. The investigators will try to match participants based on their sex, age and bodyweight, and then randomly assign these matched participants to the intervention or placebo.

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 about their supplement, electrolyte and sport drink use.