Hydration & Dehydration

Overview

Dehydration quietly erodes judgment, strength, and thermoregulation. Plan intake, watch for early signs, and treat with measured fluids and electrolytes. Balance against the risks of hyponatremia (too much plain water) and heat illness.

Skill Level: Basic

Signs and Stages

Recognize progression early to prevent spirals.

Mild (1–2% body weight loss): Thirst, dry mouth, darker urine, mild headache, decreased focus, irritability.
Moderate (3–6%): Dizziness, fatigue, rapid pulse, reduced sweat/urine, cramps, poor decisions, nausea.
Severe (≥7%): Very dark/no urine, confusion, fainting, cold clammy skin or hot dry skin, rapid breathing, shock—medical emergency.

📝 Note: Urine color is a rough guide. Aim for pale straw. Some vitamins/foods alter color—don’t rely on color alone.

Oral Rehydration

Replace fluids steadily; avoid chugging.

Volume: As a guide, 400–800 mL per hour during exertion in heat; less in cool/calm conditions. Adjust to thirst and urine output; avoid over‑drinking.
Temperature: Cool fluids (~15–20°C / 59–68°F) are absorbed well and aid cooling in heat.
Sips > gulps: Take frequent small drinks; add electrolytes when sweating heavily.

Upper limits and pacing

Most people can absorb ~0.5–1.0 L per hour during exertion; more than that can slosh and increase hyponatremia risk. Let thirst and urine guide you.
On long hot efforts, aim for a light, steady electrolyte intake rather than plain water only; pair fluids with food/salt.

⛑️ First Aid: If vomiting, try 5–10 mL every 2–3 minutes; escalate if unable to keep fluids or if mental status worsens.

💡 Tip — Estimate Your Sweat Rate: Weigh yourself (or your pack, if you prefer) before and after a one‑hour effort in similar conditions with known fluid intake. Each 0.45 kg (1 lb) lost ≈ ~0.5 L fluid deficit. Use this to plan hourly intake on future days.

Electrolytes

Sodium and potassium help retain water and support muscle/nerve function.

Practical sources: Oral Rehydration Solution (ORS), broths, a mix of water + food + a pinch of salt, commercial electrolyte powders.
Sports drinks: Often strong—consider 1:1 with water. Avoid very sugary mixes when nauseated.
Food: Crackers, soups, nuts, and fruits complement fluids.

⚠️ Caution: Hyponatremia (too much water, too little salt) mimics heat illness—headache, nausea, confusion, swelling. Favor ORS or salty snacks with water during heavy sweating.

Heat Illness Link

Hydration, rest, and cooling break the progression.

Heat cramps → Heat exhaustion → Heat stroke.
Heat exhaustion: Heavy sweating, weakness, nausea, dizziness, headache; pulse fast, skin cool/clammy. Move to shade, cool with water/evaporation, give ORS, rest.
Heat stroke (emergency): Altered mental status, hot skin (may be dry or still sweating), core temp high. Call EMS. Cool aggressively: shade, douse with water, fan vigorously; ice to neck/groin/armpits.

☑️ Checklist — Daily Hydration Plan

Start hydrated (drink with breakfast)
Carry known volumes; track intake (marks on bottle)
Add electrolytes for sustained sweat or heat
Set hourly sip reminders; check urine at breaks
Adjust pace/shade/rest by conditions

ORS (Oral Rehydration Solution) Recipe

For 1 liter of safe water:

6 level teaspoons sugar
1/2 level teaspoon salt
Mix until fully dissolved. Taste should be “not too salty.”

📝 Notes

Use level measurements; too much salt can be dangerous, too much sugar can worsen diarrhea.
Alternatives: Commercial ORS packets; sports drink diluted 1:1 with water; broth + water + crackers if that’s all you have.

Examples

Hot trail day: Sip 500 mL/h with a light electrolyte mix; 10‑minute shade rests each hour; cool hat and neck.
GI illness: Use ORS sips 5–10 mL every 2–3 minutes; escalate if lethargy, no urine 6–8 h, bloody stools, or severe dehydration signs.

Key Takeaways

Plan hydration and electrolyte intake; avoid both dehydration and over‑hydration.
Use ORS proportions precisely; small, steady sips beat chugging when ill.
Treat heat illness early with shade, cooling, and ORS; call for help with stroke signs.

Scenarios

🧭 Scenario (Exposed ridge, heat): No shade for 2 km; wind hot.
🔍 Decisions: Pace/sip cadence; electrolyte now vs later; rest timing.
✅ Outcome: You slow pace, sip 150–200 mL every 15 minutes with light electrolytes, and take 10‑minute rests each hour in micro‑shade.
🧠 Lessons: Cadence + electrolytes prevent spirals
🏋️ Drill: Mark a bottle in 100 mL increments and practice steady intake.

🧭 Scenario (GI upset): Nausea, small sips only.
🔍 Decisions: ORS mixing; micro‑doses vs gulps.
✅ Outcome: You mix ORS precisely and give 5–10 mL every 2–3 minutes; nausea eases and urine returns.
🧠 Lessons: Tiny sips win when vomiting
🏋️ Drill: Measure ORS without a spoon using packet or bottle caps (note conversions).