Water works for mild dehydration, but it’s not actually the most hydrating drink available. Beverages that contain electrolytes, a small amount of sugar, or protein keep fluid in your body longer and speed up absorption in your gut. The best choice depends on how dehydrated you are and what caused the fluid loss.
Why Some Drinks Hydrate Better Than Others
Your small intestine absorbs water fastest when sodium and glucose arrive together. A transport protein in the intestinal lining pulls one molecule of glucose and two sodium ions from the gut into the bloodstream simultaneously, and water follows. This is why plain water, which lacks both, absorbs more slowly than drinks that contain some salt and sugar. It’s also why drinking a very sugary beverage can backfire: too much sugar without enough sodium draws water into the gut instead of out of it, potentially causing loose stools.
Beyond absorption speed, how long a drink stays in your body matters. Drinks that empty from the stomach slowly release their water content into the bloodstream gradually, which prevents the brief dip in blood concentration that triggers your kidneys to flush out excess fluid. Protein and fat both slow stomach emptying, which is one reason milk outperforms most other beverages for hydration.
The Most Hydrating Drinks, Ranked
A large study measuring how much fluid people retained over several hours after drinking various beverages produced a Beverage Hydration Index. The top five, in order:
- Skim milk (retained 99% as well as or better than water)
- Oral rehydration solutions, including pediatric and sports formulas
- Whole milk
- Orange juice (95% retention compared to water)
- Water
The pattern is clear: drinks with some combination of electrolytes, protein, and a moderate amount of sugar consistently beat plain water. That said, water is still effective for everyday hydration and mild fluid loss. The differences matter most when you’re significantly dehydrated or losing fluid through sweat, vomiting, or diarrhea.
Oral Rehydration Solutions
Oral rehydration solutions (ORS) are the gold standard for treating dehydration from illness, especially when vomiting or diarrhea is involved. The formula recommended by the World Health Organization since 2002 contains 75 millimoles per liter of both glucose and sodium, with a total concentration slightly lower than blood. That precise ratio maximizes the sodium-glucose transport system in the intestine without pulling extra water into the gut.
You can buy premade versions (Pedialyte, DripDrop, and similar products), or make one at home in an emergency: mix half a teaspoon of salt and two tablespoons of sugar into about four and a quarter cups of water. Measure carefully. Too much sugar causes diarrhea, and too much salt tastes terrible and can be harmful, especially for children.
Why Milk Ranks So High
Milk’s electrolyte concentration is naturally similar to the body’s own fluids, and its carbohydrate content is comparable to commercial sports drinks. But what gives milk its edge is protein. Research by James et al. found that a solution matching the exact energy and electrolyte content of a carbohydrate drink but with added milk protein did a measurably better job at rehydrating volunteers. The protein slows stomach emptying: it takes roughly 14% longer for milk to leave the stomach compared to a sports drink with the same calories. That slower release means your kidneys don’t get a sudden flood of fluid to clear out.
Skim and whole milk performed nearly identically on the hydration index. If you tolerate dairy, a glass of milk after exercise or during a stomach illness (once you can keep food down) is a surprisingly effective rehydration choice.
Sports Drinks and When They Help
Sports drinks come in three categories based on their sugar concentration relative to blood:
- Hypotonic (under 5% carbohydrate): absorbed fastest, best for quick rehydration when you don’t need extra energy
- Isotonic (6 to 8% carbohydrate): similar concentration to blood, a middle ground between hydration and fuel
- Hypertonic (over 8% carbohydrate): absorbed slowest, designed to replenish energy stores rather than rehydrate
For pure rehydration, hypotonic drinks work best. Most popular sports drinks like Gatorade fall into the isotonic range, which is fine during prolonged exercise when you need both fluid and energy. If you’re dehydrated from illness rather than exercise, though, an ORS is a better choice because its sodium content is higher and its sugar content is more precisely calibrated.
Coconut Water
Coconut water is often marketed as a natural sports drink, and there’s some truth to it. A cup contains about 470 milligrams of potassium, which is more than a banana. But it only has around 30 milligrams of sodium per cup, which is far less than what you lose in sweat or through diarrhea. Potassium matters for hydration, but sodium is the primary electrolyte that drives water absorption in the gut.
Coconut water is a reasonable option for mild dehydration or as a between-meals drink. For significant fluid loss, you’d need to add a pinch of salt to compensate for its sodium gap.
Juice: Helpful With a Caveat
Orange juice scored just above water on the hydration index, likely because of its potassium, natural sugars, and calorie content. But full-strength fruit juice has a high sugar concentration that can cause osmotic diarrhea, which makes dehydration worse. This is especially true for apple juice, which is high in sorbitol.
The fix is simple: dilute juice 50/50 with water. A half-and-half apple juice mixture has been shown to work well for rehydrating children with mild gastroenteritis, and children tend to drink more of it than they would plain ORS because it tastes better. The same principle applies to adults. Half-strength juice gives you electrolytes and some sugar without overwhelming the gut.
Coffee and Tea
Caffeine is technically a diuretic, meaning it increases urine production. But research consistently shows that the fluid in a cup of coffee or tea more than offsets the mild diuretic effect at normal doses. Your body retains a net gain of fluid after drinking caffeinated beverages, especially if you’re a regular caffeine consumer. High doses taken all at once are more likely to cause significant fluid loss, particularly if you don’t drink caffeine regularly.
Tea actually performed well on the hydration index, roughly comparable to water. So your morning coffee or afternoon tea isn’t working against you. That said, caffeine isn’t ideal if you’re already noticeably dehydrated, since even a small diuretic nudge is counterproductive when you’re trying to restore fluid balance.
Signs Your Dehydration Needs More Than a Drink
Most mild dehydration responds well to any of the drinks above, sipped steadily over an hour or two rather than gulped all at once. Dark yellow urine, dry mouth, thirst, and mild fatigue typically improve within 30 to 60 minutes of starting to rehydrate.
Severe dehydration is different. Confusion, fainting, a rapid heartbeat, rapid breathing, complete lack of urination, or signs of shock all indicate that oral fluids alone may not be enough. These situations often require intravenous fluids in a medical setting. If someone can’t keep fluids down due to persistent vomiting, small frequent sips of an ORS (a teaspoon every few minutes) sometimes work, but escalating symptoms need professional treatment.