An oral rehydration solution (ORS) is a precise mixture of water, salts, and sugar designed to replace fluids and electrolytes lost during diarrhea or vomiting. It works faster and more effectively than water alone because its specific ratio of sodium to glucose activates a transport system in your intestinal lining that pulls water directly into your bloodstream. The World Health Organization considers it one of the most important medical advances of the 20th century, and it remains the primary treatment for mild to moderate dehydration worldwide.
How ORS Works Inside Your Gut
Your intestines absorb water by following sodium. Normally, sodium gets into your cells through several different pathways, but during a bout of diarrhea, most of those pathways shut down. The one that keeps working is a protein that moves sodium and glucose into cells together, as a pair. Neither one can cross without the other. This is the key insight behind ORS: by providing glucose and sodium in the right proportions, the solution hijacks a transport route that diarrhea can’t disable.
Once sodium and glucose cross into the intestinal cells together, water follows by osmosis. This expands the fluid volume in your bloodstream without throwing off your body’s electrolyte balance. Plain water can’t do this efficiently because it lacks the sodium and glucose needed to activate that cotransporter. And drinks with too much sugar actually make things worse by pulling water in the wrong direction, back into the intestine, which can increase diarrhea.
What’s in the Solution
Commercial ORS packets contain sodium chloride (salt), potassium chloride, glucose, and a citrate compound that helps correct the blood’s acid-base balance. The current WHO-recommended formula has a total osmolarity of 245 mOsm/L, which is slightly lower than older versions. This “low-osmolarity” formula reduces vomiting and stool output compared to earlier formulations with higher sugar and salt concentrations.
A typical ORS contains about 60 to 75 milliequivalents of sodium per liter and roughly 75 millimoles of glucose. For comparison, a standard sports drink contains around 18 mM of sodium and 5.9% carbohydrate, while ORS contains about 61 mM of sodium and 3.4% carbohydrate. Sports drinks have roughly one-third the sodium and nearly twice the sugar. That makes them poorly suited for treating diarrhea-related dehydration: too little sodium to drive proper absorption, and enough sugar to potentially worsen loose stools.
Rice-Based Formulas
Some ORS products use rice powder instead of glucose. In a randomized study of children with cholera in Bangladesh, those given rice-based ORS had 20 percent less stool output in the first eight hours of treatment compared to children given standard glucose-based ORS. The advantage was most pronounced during the early, critical phase when fluid losses are greatest. After that initial period, stool output was similar between the two groups, and electrolyte levels remained normal in both. Rice-based solutions work because the starch breaks down into glucose gradually, providing a steady supply to the sodium cotransporter while also delivering some extra calories.
When ORS Is the Right Choice
ORS is appropriate for mild to moderate dehydration caused by diarrhea, vomiting, or both. Signs of mild dehydration include a slightly dry mouth, increased thirst, and reduced urination (roughly one wet diaper or bathroom trip in six hours for children). Moderate dehydration looks more pronounced: markedly decreased urination, no tears when crying, a dry mouth, and sunken-looking eyes.
Severe dehydration, where a person is lethargic, has very sunken eyes, or can’t keep fluids down at all, typically requires intravenous fluids. ORS was developed specifically as a safer, less expensive, and more practical alternative to IV fluids for the vast majority of dehydration cases that don’t reach that severe threshold.
Using ORS With Infants and Young Children
For babies under one year, give 1 to 2 teaspoons (5 to 10 mL) of ORS every 5 to 10 minutes using a spoon or syringe. Small, frequent sips work better than large volumes because they’re less likely to trigger vomiting. If your baby is breastfeeding, continue breastfeeding. It should not be stopped during rehydration. Formula-fed infants can also continue formula mixed according to package instructions alongside ORS.
You can hold back solid food and milk (other than breast milk) for one to two days until symptoms start improving, but ORS and breastfeeding should continue throughout. Older children and adults can drink ORS freely, sipping steadily rather than gulping large amounts at once.
How to Make ORS at Home
If you can’t get to a pharmacy, you can make an emergency rehydration solution with three ingredients:
- Salt: half a level teaspoon
- Sugar: six level teaspoons
- Water: one liter of clean drinking water (about five 200 mL cups)
If your water supply isn’t reliably clean, boil it first and let it cool before mixing. The measurements need to be level, not heaping. Too much salt can be dangerous, and too much sugar can worsen diarrhea. This recipe approximates the sodium-to-glucose ratio needed to activate the intestinal cotransporter, but commercial ORS packets are more precise and also include potassium and citrate. Use the homemade version only when pre-packaged ORS isn’t available.
Storage and Shelf Life
Once you mix an ORS packet with water, the clock starts ticking. A prepared solution stored in the refrigerator stays safe for up to 24 hours. At room temperature, discard any unused solution after one hour. Bacteria grow quickly in the sugar-and-salt mixture, so it’s better to prepare smaller batches more frequently than to make a full liter and let it sit out. Unopened ORS packets, kept dry in their original packaging, last much longer and typically have an expiration date printed on the label.
Why ORS Isn’t Just Water or Juice
The most common mistake during a stomach illness is reaching for whatever liquid is nearby: water, apple juice, soda, or a sports drink. Plain water replaces volume but not electrolytes, and drinking large amounts can actually dilute your blood sodium to risky levels. Fruit juices and sodas contain far too much sugar and very little sodium, which can pull fluid into the intestine and make diarrhea worse. Sports drinks, while closer to ORS than soda, still have the wrong ratio of sugar to sodium for treating dehydration from illness.
ORS succeeds precisely because it’s boring. The formula is calibrated so that sodium and glucose arrive at the intestinal wall in nearly equal concentrations, maximizing the efficiency of that one absorption pathway that diarrhea leaves intact. That specificity is what has made it one of the most effective public health tools in modern medicine, estimated to have prevented millions of child deaths from diarrheal disease since its widespread adoption in the late 1970s.