How ORS Works, and Why the Exact Recipe Matters

When a child has diarrhoea, the danger usually isn’t the infection itself. It’s dehydration: the body losing water and salts faster than it can take them in. For decades, dehydration from diarrhoea was one of the biggest killers of young children worldwide.

The answer turned out to be astonishingly cheap: a measured mix of salt, sugar and clean water. Oral rehydration solution, or ORS, is often described as one of the most important medical advances of the twentieth century. Here’s why it works.

Why plain water isn’t enough

During diarrhoea, the gut loses not just water but also sodium, potassium and other salts that the body needs to keep its fluids in balance. Drinking plain water replaces some of the water, but not the salts, and much of it can pass straight through.

The trick: sodium and glucose travel together

The lining of the small intestine has tiny transporters that carry sodium into the body only when glucose comes with it. This system keeps working even during most diarrhoeal illnesses.

So when you drink a solution containing the right amounts of sodium and glucose:

1. Sodium and glucose are absorbed together through the gut wall.
2. Water follows them into the body, drawn by the dissolved salts.
3. The body regains both fluid and salts, and dehydration eases.

The balance matters. Too little sugar and the sodium isn’t absorbed well. Too much sugar and the extra sugar can pull water into the gut instead, making diarrhoea worse.

The balance matters. Too much sugar can pull water into the gut and make diarrhoea worse.

The WHO recipe

Since 2002, the World Health Organization and UNICEF have recommended a “reduced osmolarity” ORS. Per litre of clean water, it contains:

This mix replaced an older, stronger formula because studies found it reduced the need for unplanned drip (intravenous) treatment in children.

ORS sachets made to this formula are widely available at chemists and government health centres in India. Dissolve one sachet in exactly the amount of clean water stated on the pack, usually one litre. Using less water makes it too concentrated.

Why “energy” and “electrolyte” drinks are different

Many drinks sold in shops look like ORS, with names and packaging that suggest rehydration. But a lot of them contain much more sugar and much less salt than the WHO formula. That can make diarrhoea worse, especially in children.

In 2025, India’s food regulator FSSAI moved to stop drinks that don’t follow the WHO formula from using “ORS” in their names, after a long campaign by doctors. Because the rules have been challenged and may change, check the ingredients on the pack, not just the name. Medical ORS will say it follows the WHO formula.

When to use ORS, and when to see a doctor

ORS is used for dehydration caused by diarrhoea, vomiting or heavy sweating in the heat. For children with diarrhoea, health authorities also recommend zinc tablets alongside ORS, as advised by a doctor or health worker.

Seek medical help urgently if someone:

• can’t keep any fluids down;
• passes very little or no urine;
• is very drowsy, confused or floppy;
• has blood in their stool, a high fever or sunken eyes;
• is a baby under six months with diarrhoea.