Drinking water seems like the obvious solution to dehydration — but during gastroenteritis, intense exercise, heat exposure, or severe diarrhoea, plain water is actually less effective at restoring fluid balance than an oral rehydration solution (ORS). Understanding why, and when to use what, makes a significant practical difference.
Why ORS Works Better Than Water in Illness
The small intestine absorbs water most efficiently through a co-transport mechanism that links sodium absorption to glucose. This sodium-glucose co-transporter (SGLT1) actively pulls both sodium and water into intestinal cells and is still functional even during severe diarrhoeal illness, when the normal sodium channels may be disrupted. An ORS is formulated to exploit this mechanism — the WHO/UNICEF standard ORS provides glucose (75mmol/L) and sodium (75mmol/L) in a specific ratio that maximises SGLT1-driven absorption. Plain water, with neither glucose nor sodium, uses only passive absorption pathways, which are less efficient, particularly in the dehydrated gut. ORS was one of the most important medical discoveries of the 20th century — it transformed mortality from cholera and childhood diarrhoeal disease globally.
When ORS Is Most Important
Gastroenteritis with significant diarrhoea and/or vomiting: fluid and electrolyte losses include sodium, potassium and bicarbonate — plain water replaces none of these. Dioralyte (or own-brand equivalent) is the UK pharmacist’s first recommendation for vomiting and diarrhoea in all ages. Children under 5: particularly important — children dehydrate rapidly and ORS prevents the need for IV rehydration in many cases. Give small, frequent sips (5ml every few minutes if vomiting) rather than large amounts. Intense endurance exercise (over 90 minutes): electrolyte losses from sweat require sodium replacement alongside fluid. Isotonic sports drinks or ORS tablets dissolved in water. Heat exhaustion: salt and water losses from heavy sweating — ORS is more rapidly effective than water. Alcohol-related dehydration: alcohol causes diuresis and electrolyte losses — an electrolyte supplement before sleep is more restorative than water alone.
Using ORS Correctly
Dioralyte sachets: one sachet dissolved in 200ml of water. In gastroenteritis: replace volume lost through diarrhoea (approximately 200ml after each loose stool) plus normal maintenance fluids. Continue normal diet as tolerated — “starving a stomach bug” is unnecessary and may prolong recovery. In vomiting: 5ml every 2–3 minutes, increasing as tolerated. ORS is not appropriate undiluted or in excess — using the correct dilution maintains the sodium:glucose ratio.
Frequently Asked Questions
Can I make my own ORS at home?
WHO home recipe: 1 litre of clean water + 6 level teaspoons of sugar + ½ level teaspoon of salt. This approximates the WHO standard ORS for emergency situations. Pharmacy-prepared sachets are more accurate and convenient when available — but the home recipe is reliable and has saved millions of lives in resource-limited settings.
Is ORS the same as sports drinks like Lucozade Sport?
No — sports drinks are designed for hydration maintenance during exercise and contain lower sodium and higher carbohydrate concentrations than ORS. They are appropriate for sports hydration but not optimal for rehydration during illness. ORS has higher sodium content, optimised for maximum fluid absorption through the SGLT1 mechanism.
When should I take a child to hospital for dehydration?
Seek urgent medical attention if: the child is unable to keep any fluids down for more than 2 hours; there are signs of significant dehydration (very dry mouth, no tears when crying, sunken eyes, pale mottled skin, significantly reduced urine output — no wet nappy in 6+ hours, no urine in 8+ hours for older children); the child has blood in stool or vomit; there is high fever alongside the diarrhoea; or the child is unusually drowsy or unresponsive.
Browse Dioralyte and rehydration products at Huncoat Pharmacy. Related: Hydration Guide, Childhood Fever.
At Huncoat Pharmacy: Browse oral rehydration solutions, Travel health service, Pharmacy First.