What Is Dehydration?
Dehydration occurs when your body loses more fluid than it takes in, disrupting normal body functions. Water makes up approximately 60% of an adult's body weight and is essential for temperature regulation, nutrient transport, joint lubrication, and virtually every metabolic process. Even modest fluid losses have measurable effects on health and performance.
Warning Signs by Severity Level
Mild Dehydration (1–2% fluid loss)
- Thirst — the first noticeable sign
- Slightly darker urine (pale yellow to amber)
- Dry mouth and slightly sticky feeling
- Mild headache
- Slight fatigue and reduced concentration
- Decreased urine frequency
Moderate Dehydration (3–5% fluid loss)
- Noticeably dark yellow to amber urine
- Reduced urination (fewer than 3 times per day)
- Persistent headache
- Significant fatigue and muscle weakness
- Dizziness, especially when standing
- Dry skin that is less elastic (skin "tents" when pinched)
- Rapid heartbeat
- Reduced exercise performance
Severe Dehydration (6%+ fluid loss) — Medical Emergency
The Urine Colour Test
Urine colour is the simplest and most reliable at-home indicator of hydration status. Check your urine colour first thing in the morning and periodically throughout the day:
| Urine Colour | Hydration Status | Action |
|---|---|---|
| Clear / very pale yellow | Over-hydrated | Reduce intake slightly |
| Pale straw yellow | Well hydrated ✓ | Maintain current intake |
| Darker yellow | Slightly dehydrated | Drink 1–2 glasses now |
| Amber / honey | Moderately dehydrated | Increase intake immediately |
| Dark brown / orange | Severely dehydrated | Seek medical attention |
Note: certain foods (beetroot, asparagus), medications, and supplements (B vitamins, riboflavin) can change urine colour independent of hydration status.
Who Is Most at Risk of Dehydration?
- Elderly adults: Reduced thirst sensation and kidney efficiency; higher medication burden
- Athletes and active individuals: Can lose 1–2 litres of sweat per hour during intense exercise
- People in hot climates: Heat and humidity dramatically increase fluid loss through sweat
- Ill individuals: Fever, vomiting, and diarrhoea cause rapid fluid and electrolyte loss
- Infants and young children: Higher surface-area-to-volume ratio; less able to communicate thirst
How to Rehydrate Properly
For mild-to-moderate dehydration, water is the best rehydrating fluid. For significant dehydration from exercise or illness, oral rehydration solutions (ORS) containing sodium, potassium, and glucose are more effective than water alone at restoring fluid balance. NHS-approved products include Dioralyte. Sports drinks like Lucozade Sport are useful for exercise but contain unnecessary sugar for everyday rehydration.
Avoid caffeine and alcohol when actively rehydrating — both increase urine output and worsen fluid balance.