Oral rehydration salts (ORS) are a precise mixture of sugar, salt, and other electrolytes designed to be dissolved in clean water and drunk to treat dehydration. They work by exploiting a specific mechanism in your gut that pulls water into your body far more effectively than drinking plain water alone. The World Health Organization and UNICEF consider ORS the preferred treatment for mild to moderate dehydration caused by diarrhea, and it remains one of the most important medical interventions in global health.
What ORS Contains
A standard ORS packet contains sodium chloride (table salt), glucose (sugar), potassium chloride, and trisodium citrate. These ingredients are measured in exact proportions so the final solution, once mixed with the correct volume of water, hits a specific concentration. The current WHO-recommended formula targets a total osmolarity of 245 mOsm/L, which is a measure of how concentrated the dissolved particles are. This replaced an older formula with a concentration of 311 mOsm/L after studies showed the lower-osmolarity version worked better and caused less vomiting.
The ratio of glucose to sodium matters enormously. The two need to be present in roughly equal molecular concentrations for the absorption mechanism to work properly. Too much sugar and you get a solution that can actually worsen diarrhea by drawing water into the gut. Too little, and the transport system doesn’t activate efficiently.
How Sugar and Salt Pull Water Into Your Body
The reason ORS works so well comes down to a protein called SGLT1, a transporter embedded in the lining of your small intestine. This transporter acts like a molecular pump: it grabs two sodium ions and one glucose molecule from the fluid in your gut and moves them together across the intestinal wall into your bloodstream. Without glucose present, sodium can’t be actively absorbed this way. Without sodium, the glucose won’t move either. They depend on each other.
Once sodium and glucose cross the intestinal wall, water follows automatically through osmosis. This process works even when the gut is damaged by infection, which is why ORS can rehydrate someone with severe diarrhea when plain water would largely pass straight through. A 1978 editorial in The Lancet called this discovery “potentially the most important medical advance of this century” because it meant dehydration from cholera and other diarrheal diseases could be treated without intravenous fluids in most cases.
When ORS Is Used
ORS is designed for mild to moderate dehydration, particularly from diarrhea caused by gastroenteritis. This covers the vast majority of dehydration cases in both children and adults. Signs that ORS is appropriate include increased thirst, dry mouth, reduced urine output, slight dizziness, and in children, fewer wet diapers and crying without tears.
Severe dehydration is a different situation. If someone is unable to drink, extremely lethargic, or showing signs of shock (very rapid heartbeat, cold hands and feet, no urine output for many hours), they typically need intravenous fluids to recover fast enough. ORS can be started alongside IV treatment once the person is able to swallow.
Beyond diarrheal illness, ORS is useful for dehydration from heavy sweating, vomiting, or heat exposure. It’s a staple in emergency kits, travel medicine, and humanitarian aid supplies.
ORS vs. Sports Drinks
Sports drinks and ORS are not the same thing, even though both contain electrolytes. The differences in formulation are significant. A typical ORS contains about 60.9 millimoles per liter of sodium and 3.4% carbohydrate. A typical sports drink contains only 18.4 millimoles per liter of sodium and 5.9% carbohydrate. In other words, sports drinks have roughly one-third the sodium and nearly twice the sugar.
That composition makes sports drinks fine for replacing sweat losses during exercise but poorly suited for treating actual dehydration from illness. The lower sodium content means they don’t drive the SGLT1 transport mechanism as effectively, and the higher sugar concentration can worsen diarrhea. If you’re dealing with a stomach bug, ORS is the right choice. If you’re finishing a run on a hot day and feeling fine, a sports drink or plain water will do.
How to Mix and Use ORS
Commercial ORS packets come with instructions specifying exactly how much water to add, usually one liter per packet. The key rule is to follow the directions precisely. Adding too little water makes the solution overly concentrated, which can pull fluid into the gut and make things worse. Adding too much water dilutes it below the threshold where the absorption mechanism works efficiently.
For children with mild to moderate dehydration, the general approach is to offer small, frequent sips rather than large amounts at once. A teaspoon or tablespoon every few minutes works better than a full cup, especially if the child is also vomiting. Adults can drink more freely but should still pace themselves if nausea is a problem.
Once mixed, the solution should be used within 24 hours. After that, discard it and prepare a fresh batch. You can store it at room temperature or in the refrigerator during that window. Some people find it more palatable when chilled.
Making ORS at Home
If you can’t get commercial ORS packets, you can make an emergency version with three ingredients:
- 4 cups of clean water
- ½ teaspoon of table salt
- 2 tablespoons of sugar
Stir until the salt and sugar dissolve completely. This recipe, recommended by the University of Virginia Health System, approximates the sodium-to-glucose ratio needed to activate intestinal absorption. It won’t contain potassium or citrate like commercial formulas, so it’s a stopgap rather than a perfect substitute. The measurements need to be accurate. Too much salt tastes unpleasant and can be harmful, especially for young children. Too much sugar reduces effectiveness and can worsen diarrhea.
Commercial packets are always preferable when available because the concentrations are exact and they include the full range of electrolytes. But in a pinch, the homemade version works and has saved countless lives in low-resource settings where packets weren’t immediately on hand.
Why ORS Works Better Than Water Alone
Plain water does get absorbed in your intestines, but it relies on passive mechanisms that are slow and inefficient when the gut lining is inflamed or damaged by infection. Diarrheal pathogens disrupt the normal absorption pathways, so much of the water you drink passes through without being absorbed. ORS bypasses this problem by activating the sodium-glucose cotransporter, which remains functional even in a damaged gut. The result is faster, more reliable fluid absorption when you need it most.
This is also why drinking large quantities of plain water during a diarrheal illness can actually be counterproductive. Without electrolytes, you risk diluting the sodium already in your blood, a condition that causes its own set of problems including headache, confusion, and in extreme cases, seizures. ORS replaces both the water and the electrolytes you’re losing, keeping your body’s chemistry in balance while restoring fluid volume.