ORS stands for oral rehydration solution, a precise mixture of salts, sugar, and water designed to treat dehydration faster and more effectively than water alone. Developed as a standard formula by the World Health Organization and UNICEF, it works by exploiting a specific transport mechanism in your small intestine that pulls water into your body when glucose and sodium are present together in the right ratio. ORS has been credited with preventing up to 93% of deaths from diarrheal dehydration and is considered one of the most important medical advances of the 20th century.
What’s Actually in ORS
The current WHO formula is designed to be mixed with one liter of clean water. It contains 2.6 grams of sodium chloride (table salt), 1.5 grams of potassium chloride, 2.9 grams of trisodium citrate, and 13.5 grams of glucose. These ingredients aren’t random. Each one serves a specific function: sodium and potassium replace the electrolytes lost through vomiting or diarrhea, glucose drives the absorption mechanism, and citrate helps correct the acid-base imbalance that dehydration causes.
You can buy ORS as pre-measured packets or as ready-to-drink bottles at most pharmacies. The packets are simply torn open, poured into a liter of water, and stirred until dissolved. The resulting drink tastes mildly salty and slightly sweet.
How It Works in Your Body
Plain water can rehydrate you, but it doesn’t replace lost electrolytes, and your intestines absorb it relatively slowly. ORS takes advantage of a protein in the lining of your small intestine that acts like a revolving door: it only lets glucose in when sodium comes along with it. When glucose and sodium pass through together, water follows automatically by osmosis. This cotransport mechanism works even when your gut is inflamed from infection, which is why ORS is so effective during illness.
The ratio matters. Too much sugar overwhelms the system and actually pulls water into the intestine instead of absorbing it, making diarrhea worse. Too little glucose means the transport mechanism doesn’t activate efficiently. The WHO formula is calibrated to hit the sweet spot.
Why ORS Instead of Sports Drinks or Juice
Sports drinks, sodas, and fruit juices are not substitutes for ORS. The differences in composition are significant. A typical sports drink contains about 458 mg of sodium per liter, while ORS contains roughly 1,330 mg per liter, nearly three times as much. Potassium tells a similar story: 125 mg per liter in sports drinks versus 780 mg in ORS. Meanwhile, sports drinks pack in almost twice the sugar (59 grams per liter compared to 33 grams in ORS).
That extra sugar and lower sodium concentration means sports drinks can’t activate the cotransport mechanism as effectively. The excess carbohydrate can even cause additional fluid loss through osmotic effects in the gut. Sports drinks were engineered for sweating athletes, not for someone losing fluids through vomiting or diarrhea. They solve a different problem.
When You Need ORS
ORS is recommended for mild to moderate dehydration, particularly when fluid loss comes from diarrhea, vomiting, or both. In mild dehydration (roughly a 5% fluid loss in infants), you might notice slightly dry mouth, increased thirst, and reduced urination. Moderate dehydration (around 10% fluid loss) brings more obvious signs: noticeably dry mouth, rapid heart rate, very little urine output, sunken eyes, lethargy, and skin that doesn’t bounce back quickly when pinched.
ORS is especially critical for young children. Diarrhea remains the second leading cause of death in children under five worldwide, killing approximately 525,000 children each year. The vast majority of those deaths, about 90%, occur in Sub-Saharan Africa and South Asia, often in areas with limited access to clean water and healthcare. Despite its proven effectiveness, 62% of children in low- and middle-income countries still don’t receive ORS when they need it.
ORS isn’t appropriate when someone is vomiting so heavily they can’t keep fluids down, or when there’s an intestinal obstruction. In those cases, intravenous fluids are necessary instead.
How Much to Give
For rehydration in children, the general guideline is 50 to 100 milliliters of ORS per kilogram of body weight, given over three to four hours. A 10-kilogram toddler, for example, would need 500 to 1,000 milliliters during that window. After the initial rehydration phase, ongoing losses need to be replaced: roughly 10 milliliters per kilogram for each watery stool, and about 2 milliliters per kilogram for each episode of vomiting.
For adults, the approach is simpler. Sip ORS frequently after each loose stool or vomiting episode. Small, frequent sips tend to stay down better than gulping large amounts at once, which is particularly important if nausea is still present.
Making ORS at Home
If you can’t get to a pharmacy, you can make a basic rehydration solution with household ingredients. Mix four cups of clean water with half a teaspoon of table salt and two tablespoons of sugar. Stir until everything dissolves completely. This won’t contain potassium or citrate like the full WHO formula, but it activates the same glucose-sodium cotransport mechanism and is far better than plain water when you’re dehydrated from illness.
Precision matters here. Too much salt can be dangerous, especially for children. Measure carefully rather than estimating, and use level spoonfuls rather than heaping ones. If the solution tastes saltier than tears, there’s too much salt.
Storage and Safety
Once mixed, ORS doesn’t last long. At room temperature, a prepared solution should be used or discarded within 12 hours. Refrigerated, it stays safe for up to 24 hours. After that, bacterial growth makes it unsafe to drink. If you’re using packets, mix only as much as you expect to use in that time window. Unopened packets stored in a cool, dry place remain shelf-stable for much longer, typically one to two years depending on the manufacturer.
Always use clean water for mixing. If your tap water isn’t safe to drink, boil it first and let it cool before adding the ORS powder. Using contaminated water defeats the purpose entirely, since waterborne pathogens are often what caused the dehydration in the first place.