| What it is | Losing more fluid than you take in |
| Signs | Thirst, dark urine, headache, fatigue |
| Raises risk of | Heat illness, poor performance |
| Prevent with | Steady fluids + electrolytes |
Dehydration is a harmful deficit of body fluids that occurs when you lose more water (through sweat, breathing, and urine) than you take in. On the trail it causes thirst, dark urine, headache, fatigue, and dizziness, reduces performance, and raises the risk of heat illness. Prevention is steady drinking and replacing electrolytes on long, hot, or high-output days.
This is general educational information, not medical advice.
Balance, not just water
Pair water with electrolytes to avoid the opposite problem, hyponatremia; dehydration also fuels heat exhaustion. Treat your water — see water treatment.
Frequently asked questions
What are the signs of dehydration?
Thirst, dark yellow and reduced urine, dry mouth, headache, fatigue, dizziness or lightheadedness, and decreased performance. A practical field check is urine color — pale straw suggests good hydration, dark amber suggests you need to drink more. Severe dehydration causes rapid heartbeat and confusion.
How much water should you drink while hiking?
Needs vary with heat, exertion, altitude, and body size, but a common guideline is roughly half a liter (about 2 cups) per hour of moderate activity in moderate heat, more when it's hot or strenuous. Drink steadily rather than waiting for thirst, and pair water with food or electrolytes on long efforts to avoid hyponatremia.
Why is dehydration dangerous outdoors?
Beyond making you feel awful and perform poorly, dehydration impairs your body's ability to cool itself, raising the risk of heat exhaustion and heat stroke, and clouds judgment, which leads to mistakes. It can also worsen altitude illness. Staying hydrated is a core part of backcountry safety.
Sources
- Hydration & heat — CDC
- Wilderness hydration — Wilderness Medical Society