Reviewed by Emily Carter, MSc, RD
Registered Dietitian & Hydration Research Specialist. Emily holds a Master of Science in Human Nutrition and has spent over a decade translating nutrition research into practical, evidence-based guidance for everyday health and athletic performance.
How to Stay Hydrated When Sick: The Recovery Protocol
How to Stay Hydrated When Sick: Quick Answer
Illness increases fluid loss through fever (sweating), vomiting, diarrhoea, and increased respiratory rate. The target increases to 3L+ daily during most illnesses. Small, frequent sips are better tolerated than large volumes when nauseous. Electrolytes are essential during gastrointestinal illness — plain water isn't sufficient when losing fluid through vomiting or diarrhoea. Seek medical attention if unable to keep fluids down for 24 hours, signs of severe dehydration appear, or symptoms worsen despite hydration.
Why Illness Increases Hydration Needs
Fever
Every 1°C increase in body temperature increases fluid loss by approximately 10–15%. A fever of 39°C (2°C above normal) increases fluid loss by approximately 20–30% above baseline. Sweating from fever compounds this.
Per degree Celsius above 37°C: Add 500mL to your daily baseline.Respiratory Illness (Cold, Flu)
Increased breathing rate and mouth breathing significantly increase respiratory fluid loss. Congestion that forces mouth breathing doubles respiratory water loss compared to nasal breathing. A respiratory illness can add 300–500mL of daily fluid loss above baseline.
Vomiting and Diarrhoea
The most serious illness-related hydration scenario. Each episode of vomiting or significant diarrhoea can represent 200–400mL of fluid loss plus electrolyte loss (sodium, potassium, chloride). Multiple episodes rapidly compound into significant dehydration and electrolyte imbalance.
Research context: The World Health Organization (WHO) oral rehydration solution (ORS) was developed specifically for this scenario — a clinically formulated blend of sodium, glucose, potassium, and water that replaces both fluid and electrolytes more effectively than plain water.Sick Hydration by Illness Type
Cold and Flu
Target: Normal daily baseline + 500–750mL for fever and respiratory loss Best fluids:- Water (primary)
- Warm herbal teas (soothing, counts toward intake, no caffeine)
- Clear broth (sodium + fluid + warmth)
- Honey-lemon water (soothing, vitamin C, mild antibacterial)
- Electrolyte drinks (low sugar, particularly if sweating significantly)
Stomach Illness (Vomiting/Diarrhoea)
Target: Replace fluid + electrolytes from every episode of loss Best approach — the 20-minute rule:- After vomiting: wait 20 minutes before attempting to drink
- Start with ice chips or 1–2 sips every 5–10 minutes
- Gradually increase to small amounts (50–100mL) every 15–20 minutes
- Use ORS (Pedialyte, WHO formula) rather than plain water — electrolyte replacement is critical
Urinary Tract Infections (UTIs)
Target: Increase to 2.5–3L daily minimum Mechanism: High urine volume flushes bacteria from the urinary tract before they can re-colonise. Per a 2018 randomised trial in JAMA Internal Medicine, women with recurrent UTIs who increased water intake by 1.5L daily had a 48% reduction in UTI recurrence over 12 months.Wide Mouth for Sick-Bed Sipping
The Mammoth Mug 2.5L — wide mouth for electrolyte tablets and lemon additions, 2.5L to keep you on track through a full sick day, Tritan (BPA-free, DEHP-free). Canadian brand at Sport Chek.
When Hydration Alone Isn't Enough
Seek medical attention if:- Unable to keep any fluids down for 24 hours in adults (12 hours in children)
- Signs of severe dehydration: no urination for 8+ hours, extreme dizziness, rapid heartbeat, confusion
- High fever (above 39.5°C) that doesn't respond to OTC medication
- Blood in vomit or stool
- Symptoms of an infant or elderly person with GI illness (both are high-risk for rapid severe dehydration)
Oral rehydration is appropriate for mild-to-moderate illness dehydration. Severe dehydration may require IV fluids — that's a hospital decision.
Caring for Others: Paediatric and Senior Hydration During Illness
Children: Children dehydrate faster than adults. The signs to watch for: no tears when crying, dry mouth, no urination for 6+ hours, sunken eyes or fontanelle (infants). Use Pedialyte or similar ORS. Avoid sports drinks (too much sugar) and pure fruit juice (too much sugar, not enough sodium). Seniors: Seniors have reduced thirst sensation and impaired kidney concentration ability. They may appear less distressed by dehydration while being significantly dehydrated. Proactively offer fluids every 30–60 minutes during illness regardless of thirst expression.Recover Faster. Hydrate Right.
The Mammoth Mug 2.5L — 2.5L for illness recovery hydration, wide mouth for ORS tablets and lemon, Tritan (BPA-free, DEHP-free, EA/AA-free). Canadian brand since 2014. At Sport Chek.
Frequently Asked Questions
How much water should I drink when sick?
Your normal daily baseline (body weight × 35mL) plus 500mL per degree Celsius of fever above 37°C. For most illnesses: 3L+ from all fluid sources. For GI illness with vomiting/diarrhoea: replace each episode with ORS.
What should I drink when sick?
Water (primary), warm herbal tea, clear broth, honey-lemon water for respiratory illness. Oral rehydration solution (Pedialyte, WHO ORS) for vomiting/diarrhoea — plain water isn't sufficient for GI illness.
Can you drink too much water when sick?
Yes — especially with GI illness. Excessive plain water without electrolytes during vomiting/diarrhoea can cause hyponatremia (low blood sodium). Use ORS instead of plain water when experiencing significant fluid loss.
Why should I use Pedialyte instead of water for stomach flu?
Stomach illness causes fluid loss that contains electrolytes (sodium, potassium, chloride) — not just water. Plain water replaces the water but not the electrolytes. Per WHO ORS research, oral rehydration solution replaces both and is significantly more effective for preventing serious dehydration.
Does drinking more water help you recover faster from a cold?
Adequate hydration supports immune function and mucus production (which traps and expels pathogens). It doesn't directly fight viruses. However, dehydration from fever and respiratory illness impairs recovery — staying hydrated removes this impediment.
How do I stay hydrated when I can't keep water down?
The 20-minute rule: wait 20 minutes after vomiting before attempting to drink. Start with ice chips or 1–2 sips every 5–10 minutes. Gradually increase. Use ORS (Pedialyte) rather than plain water for better electrolyte replacement and tolerance.
When should I see a doctor for dehydration during illness?
If unable to keep fluids down for 24 hours (12 hours for children), signs of severe dehydration (no urination 8+ hours, extreme dizziness, confusion), or high fever not responding to OTC medication. Severe dehydration may require IV fluids.
Does chicken soup really help when sick?
Yes — there's supporting evidence beyond folk medicine. A 2000 study in Chest found chicken soup inhibited neutrophil migration (reducing inflammation) and provided sodium, fluid, and warmth. The broth contributes to fluid and electrolyte intake. The warm steam supports respiratory mucosal function.
