Michael Turner
Baseline planning: for cool-to-mild conditions and easy-to-moderate pace, assume 2–4 L in a 24-hour window. If ambient temperature exceeds ~25°C / 77°F, pace is brisk, or load is heavy, budget 3–6 L. At elevations above ~2,500–3,000 m add ~0.5 L for every extra 1,000 m of altitude due to increased respiratory fluid loss.
Sweat-rate technique: weigh yourself nude immediately before and after one hour of typical trail effort without drinking. Weight loss in kilograms ≈ liters lost. Use that value to set a drinking target for similar conditions, aiming to replace about 75–100% of measured losses. Example: a 0.8 kg loss in one hour indicates ~0.8 L lost; plan to sip roughly 0.6–0.8 L each hour under matching intensity.
Carrying and resupply: bring a primary reservoir of 1.5–2 L (bladder or bottles) and a contingency capacity of 1–3 L if sources are sparse. If the next reliable source is more than ~6 hours of continuous travel away, top up an extra 1–2 L. Treat or filter natural sources and factor treatment time and fuel for melting or boiling into your supply plan.
Electrolytes and practical cues: use electrolyte mixes for outings longer than 2–3 hours of steady exertion; aim for formulations that supply roughly 300–700 mg sodium per liter of fluid for sweat replacement. Signs of inadequate intake include dark urine, lightheadedness, decreased performance and reduced urine frequency; signs of excess include persistent very-clear urine and swelling. Pre-load with ~0.5 L in the two hours before starting, and sip small amounts regularly–about 150–250 mL every 15–20 minutes during intense activity–to maintain steady balance.
Estimate fluid requirements from body mass, sweat rate and planned mileage
Aim for a baseline of 30–35 ml of fluid for each kilogram of body mass across a 24‑hour span, plus replacement of measured sweat loss during active hiking (typical range 0.5–1.0 L each hour of moderate effort); add a safety reserve of 0.5–1.0 L.
Straightforward calculation steps
- Baseline need: multiply body mass (kg) by 0.030–0.035 to get liters for a 24‑hour span. Example: 75 kg × 0.035 = 2.63 L.
- Planned hiking hours: divide planned miles by expected pace (mph) to get hours of sustained exertion. Example: 20 miles ÷ 3 mph = 6.7 hours.
- Sweat-rate test (field method): pre‑hike body mass (kg) minus post‑hike mass (kg), add volume of fluid consumed (L) and subtract urine output (L); divide result by hiking hours to get L each hour.
- Formula: sweat rate = (pre‑mass − post‑mass + fluid consumed − urine output) ÷ hours
- Example: 75.0 kg → 74.0 kg, drank 1.0 L, no urine = (75−74 + 1.0 − 0) ÷ 3 = 0.67 L each hour.
- Total required for 24‑hour span: baseline + (sweat rate × hiking hours) + safety reserve. Example: 2.63 L + (0.67 × 6.7) + 0.5 ≈ 7.2 L.
Practical carry strategy and adjustments
- If reliable refill points are spaced, calculate segment load: carry enough for hiking hours until the next source plus 0.5–1.0 L reserve. Example: next source in 10 miles at 3 mph → 3.33 hours × 0.67 L each hour ≈ 2.2 L, carry ~3.2 L to be safe.
- Adjust upward by multipliers from 1.1 to 1.5 in hot conditions, at high altitude, or with heavy clothing and long uphill sections; reduce slightly for cool, shaded, low‑intensity hikes.
- Electrolyte guidance: replace sodium at roughly 300–700 mg for every liter of fluid lost during exercise; consider concentrated electrolyte tabs or powders rather than high‑volume sports drinks.
- Container plan: combine a reservoir plus one or two bottles so volume can be shed as it is consumed; mark target volumes for key resupply points on the route.
Adjust intake for temperature, elevation, humidity and heavy exertion
Immediate rule: increase baseline fluid targets by 250–500 ml for each 10°C above 20°C, add 300–600 ml for each 1000 m of elevation gain above 1500 m, and plan for 500–1000 ml each hour during sustained high-intensity work longer than 5 hours. Combine these adjustments rather than applying them in isolation.
Temperature and humidity
Hot, dry conditions: expect higher evaporative loss but faster evaporation so sweat may feel less; add 250–400 ml for each 5–10°C rise above 20°C and sip steadily (100–250 ml every 15–20 minutes during activity). High relative humidity (>60%): evaporation drops and sweat rates climb–add 100–300 ml for each 10% RH rise above 60% and favor cool, shaded breaks to lower ongoing loss.
Elevation and heavy exertion
Altitude effects: increase breathing losses and insensible loss; add 300–600 ml for each 1000 m above 1500 m (example: at 3500 m add ~600–1200 ml). Heavy work: for exertion producing >600–800 kcal each hour aim for 500–1000 ml each hour total, including fluids with electrolytes.
Electrolytes and rehydration strategy: during long sweaty sections target sodium intake of ~300–700 mg each hour; use concentrated sports mixes or salt tablets if plain fluids dominate. Limit plain hypotonic liquids to about 1.0–1.2 L each hour; if intake must exceed that, increase sodium and carbohydrate to support absorption and reduce hyponatremia risk. After a hard segment, replace 1.2–1.5 L for each kg of body mass lost within the first 2–4 hours.
Practical kit tip: carry a bladder sized to match high-demand stretches and bring at least one insulated bottle for warm climates; consider pack choices and tracking accessories shown at best luggage for carrying suits and best luggage tracker for international travel android.
Decide quantity to carry: fill strategy, filter/treatment limits and source spacing
Carry a working reserve of 2–3 L of treated fluid between reliable sources; increase to 4–6 L when source intervals exceed 12 km (7.5 mi), temperatures exceed 30 °C (86 °F) or heavy exertion is expected. Remember: 1 L ≈ 1 kg ≈ 2.2 lb.
Container strategy: dual-container systems reduce risk – common setups that balance weight and redundancy: 1) 2 L bladder + 1 L hard bottle (primary + reserve); 2) two 1 L soft flasks + 1 L hard bottle (easy sipping + emergency); 3) 3 L bladder + 0.5 L bottle (high capacity with small emergency). Stow the reserve bottle in an accessible pocket and keep bladder bite valve insulated in cold conditions.
Filter and treatment limits: hollow-fiber/ceramic filters typically 0.1–0.2 µm (remove bacteria and protozoa, not viruses), flow 0.5–2 L/min, lifetime ~200–2,000 L depending on model and turbidity; pump filters often rated 1,000–2,000 L; bottle-integrated filters: 100–400 L. Chemical oxidizers (chlorine dioxide) usually treat ~1 L per dose, clear liquid contact time ~30 minutes, cold/turbid contact up to 4 hours; iodine formulations require longer for protozoa and are contraindicated for some users. UV pen devices treat ~0.5–1 L per cycle (roughly 45–90 seconds per L) with 30–100 treatments per full charge or battery set. Carry spare batteries or a backup chemical option for long trips.
Source-spacing rules of thumb: gaps under 5 km (3 mi) – keep 0.5–1 L reserve; gaps 5–12 km (3–7.5 mi) – carry 1.5–3 L; gaps over 12 km (7.5 mi) – carry 3–6 L and include a backup treatment method. Multiply planned carried volume by 1.25–1.5 when routes include steep climbs, exposed heat, slow streams or unreliable flow.
Practical planning: identify reliable springs/creeks on maps/GPS and mark flow reliability. If the next confirmed source is 10 km away and expected intake is ~2 L in 24 hours, pack 3–4 L (planned intake + 50% contingency) and ensure treatment capacity equals at least twice that carried volume. For multi-day sections with sparse sources, bring treatment supplies rated for total expected liters plus 50% reserve.
Recognize early dehydration signs and step-by-step on-trail remedies
Recommendation: Sip 150–250 ml of electrolyte-containing fluid every 10–20 minutes during sustained exertion; increase intake to 300–450 ml each hour when sweat loss approaches ~1 L each hour or ambient temperature exceeds 25°C.
Early signs: dry mouth; persistent thirst; urine dark amber or resembling apple juice; urination fewer than 2–3 times within 12 hours; urine volume under 30–40 ml each hour while active; headache; lightheadedness on standing; dizziness; sudden performance drop; muscle cramps; heart rate elevated above usual by 15–25 bpm; reduced sweating despite heat; mild nausea.
Step 1 – Immediate halt and assessment: Stop moving, move to shade or sheltered spot, sit or lie with feet slightly elevated for 5–10 minutes, check mental clarity and pulse rate.
Step 2 – Controlled rehydration: Take small, frequent sips: 50–150 ml every 10 minutes for the first 30–60 minutes; aim for 500–1,000 ml total in that hour depending on symptom severity. Avoid gulping large volumes at once if nausea is present.
Step 3 – Electrolyte replacement: Prefer commercial oral rehydration salts or sports drinks with ~300–700 mg sodium per liter; if unavailable, mix 6 level teaspoons sugar + 1/2 level teaspoon table salt in 1 L of clean fluid (standard simple ORS). Electrolyte tablets (sodium 200–400 mg per dose) are compact and effective for ongoing use.
Step 4 – Cooling and rest: Remove heated layers, apply cool wet cloths to neck/wrists, fan skin, avoid further uphill movement until pulse and symptoms stabilize. For heat-induced faintness, mist skin and target core temperature reduction below 38.5°C.
Step 5 – Monitor response: Reassess every 15–30 minutes: pulse returning to near-normal, urine color lightening toward pale straw, mental clarity restored, cramps easing. If symptoms improve, reduce pace and continue scheduled sipping and electrolyte dosing.
Evacuation triggers: confusion, collapse or loss of consciousness; persistent vomiting that prevents oral intake; inability to produce measurable urine after 1 hour of rehydration (120 bpm with hypotension (systolic <90 mmHg); core temperature above 39°C. Seek professional medical aid or emergency evacuation in these cases.
Practical kit items to carry: portable electrolyte packets, small measuring bottle or marked container for controlled sips, ORS sachets, blister-proof salt tablets, compact thermometer or pulse check method, waterproof bag for electronics. Check device security and connectivity before setting out: are dlink cameras secure.
Note: If rehydration attempts fail or symptoms escalate, prioritize rapid descent to lower temperature and faster access to medical care; intravenous fluids may be required for severe deficits.
