Signs of dehydration.

Even mild dehydration — just 1–2% of body weight — can impair physical and cognitive performance. Know the signs before they become serious.

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Dehydration by severity.

Mild (1–2% fluid loss)

  • Thirst — your body's first signal (often already too late)
  • Dry mouth and slightly sticky saliva
  • Dark yellow urine — should be pale straw yellow
  • Reduced urine frequency (less than 4× per day)
  • Mild headache
  • Slight fatigue

Moderate (3–5% fluid loss)

  • Strong, persistent headache
  • Significant fatigue and reduced exercise performance
  • Difficulty concentrating and brain fog
  • Rapid heartbeat (tachycardia)
  • Reduced sweating in hot conditions
  • Muscle cramps
  • Nausea

Severe (>5% fluid loss) — Seek medical help

  • Extreme thirst
  • Very dark or no urine output
  • Sunken eyes
  • Rapid, weak pulse
  • Confusion or delirium
  • Loss of skin elasticity (poor skin turgor)
  • Fainting or loss of consciousness

How to rehydrate quickly.

1.

Drink water immediately

Start with 500ml of cool (not ice cold) water. Cold water is absorbed faster than warm water.

2.

Add electrolytes for moderate dehydration

For fluid loss from exercise or heat, add electrolytes (sodium, potassium) via sports drink or electrolyte tablets.

3.

Eat water-rich foods

Cucumber (96% water), watermelon (92%), strawberries (91%), and celery (95%) accelerate rehydration alongside drinking.

4.

Avoid diuretics temporarily

Limit coffee, alcohol, and energy drinks until rehydrated. These compounds increase urine output and worsen dehydration.

5.

Rest in a cool environment

Reduce sweat rate by moving out of heat. Cooling your body reduces further fluid loss while you rehydrate.

Prevention is better than cure.

Calculate your exact daily water needs to prevent dehydration before it starts.

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