Rehydration salts are a precise mixture of sugar, table salt, and a few other minerals that, when dissolved in water, replace fluids and electrolytes lost during diarrhea, vomiting, or heavy sweating far more effectively than water alone. The standard formula, recommended by the World Health Organization and UNICEF, has a total osmolarity of 245 mmol/L, a concentration carefully calibrated to maximize absorption in the gut. It’s considered one of the most important medical advances of the 20th century, preventing millions of deaths from dehydration each year.
What’s in the Packet
A standard oral rehydration salts (ORS) packet is designed to be mixed with one liter of clean water. It contains four ingredients, each measured in grams per liter: 13.5 g of glucose (a simple sugar), 2.6 g of sodium chloride (table salt), 1.5 g of potassium chloride, and 2.9 g of trisodium citrate. That’s it. The glucose is the largest component by weight, and for good reason: it’s not there for energy or taste. It’s there because it drives the absorption mechanism that makes the whole solution work.
The potassium replaces what’s lost through diarrhea and vomiting, which can strip the body of this mineral quickly. The citrate acts as a base to help correct the acid buildup that often accompanies severe dehydration. Every ingredient serves a specific physiological role, and changing the ratios can reduce effectiveness or cause harm.
How Rehydration Salts Actually Work
The reason plain water is a poor treatment for dehydration from diarrhea is that the intestine can’t absorb it efficiently on its own, especially when inflamed. Rehydration salts exploit a specific transport protein in the lining of the small intestine. This protein pulls glucose from the gut into intestinal cells, and for every molecule of glucose it moves, it carries two sodium ions along with it. Water then follows the sodium passively, drawn across the intestinal wall by osmotic pressure.
This is why the glucose-to-sodium ratio matters so much. Too much sugar overwhelms the system and can actually pull water into the gut, worsening diarrhea. Too little sugar means fewer transport proteins are activated, and absorption slows. The current low-osmolarity formula, adopted globally in 2001, reduced sugar and salt concentrations compared to the original 1970s version. The result: less stool output, shorter duration of diarrhea, and less need for IV fluids.
ORS vs. Sports Drinks
Sports drinks and rehydration salts are not interchangeable. A typical sports drink contains about 18 mM of sodium and nearly 6% carbohydrate (sugar). A medical-grade ORS contains roughly 61 mM of sodium and only about 3.4% carbohydrate. That means sports drinks have about a third of the sodium and nearly twice the sugar of ORS. Sports drinks are designed to fuel exercise and replace sweat losses, which are relatively mild compared to the fluid and electrolyte losses from illness. If you’re dealing with diarrhea or vomiting, a sports drink won’t rehydrate you nearly as well, and the excess sugar can make diarrhea worse.
How to Prepare and Store the Solution
Mix one packet with exactly the amount of clean water specified on the label, typically one liter. Using too little water makes the solution dangerously concentrated; using too much dilutes it below the effective threshold. Stir until fully dissolved. Don’t add anything else: no extra sugar, no juice, no flavoring. These change the osmolarity and can undermine the absorption mechanism.
Once mixed, the solution stays safe for 12 hours at room temperature or 24 hours if refrigerated. After that, discard it and make a fresh batch. Bacteria grow readily in sugar-salt solutions at room temperature, so don’t push these limits.
Giving ORS to Children
Children dehydrate faster than adults and are the primary beneficiaries of ORS worldwide. For a child with mild dehydration, the general guideline is roughly 50 to 60 mL per kilogram of body weight over four hours. For moderate dehydration, that increases to 80 to 100 mL per kilogram over the same period. For a 10-kilogram toddler (about 22 pounds) with mild dehydration, that works out to roughly 500 to 600 mL, or about two to two and a half cups, sipped gradually over four hours.
Small, frequent sips work better than large gulps, especially if the child is vomiting. A teaspoon or tablespoon every few minutes is often more effective than offering a full cup. If the child vomits, wait 10 to 15 minutes and try again. Most children will keep down small amounts even when nauseous.
Making a Homemade Solution in an Emergency
If you can’t get commercial ORS packets, you can make a basic version at home. The University of Virginia Health recipe calls for 4 cups of clean water, half a teaspoon of table salt, and 2 tablespoons of sugar. Stir until completely dissolved. This won’t include potassium or citrate, so it’s less complete than a commercial formula, but it will activate the same glucose-sodium absorption pathway and is far better than plain water.
Accuracy matters here. Too much salt is dangerous, particularly for young children. If you’re unsure of your measurements, err on the side of slightly less salt rather than more. Taste the solution before giving it: it should taste roughly like tears, slightly salty but not unpleasant. If it tastes saltier than that, add more water.
Who Should Be Cautious
For the vast majority of people, ORS is safe and effective. The notable exception is anyone with impaired kidney function. In people with acute kidney injury or chronic kidney disease, the kidneys can’t properly filter the extra sodium and potassium, which can lead to dangerous electrolyte buildup or fluid overload. People with high blood pressure or reduced urine output should also be cautious. If you have known kidney problems and need rehydration, medical supervision ensures the electrolyte load is adjusted to what your kidneys can handle.