The best rehydration drink depends on why you’re dehydrated, but the top performers across research are skim milk, oral rehydration solutions (ORS), and full-fat milk. In a landmark study published in the American Journal of Clinical Nutrition, researchers tested 13 common beverages and found that skim milk kept the body hydrated 58% longer than water, while ORS came in just behind at 54% longer. Plain water, despite being the go-to choice, ranked near the bottom for fluid retention.
That ranking surprises most people. The reason comes down to what else is in the drink besides water, and how your gut responds to it.
Why Some Drinks Hydrate Better Than Water
Your body doesn’t absorb and hold onto every drop of fluid you drink. Much of it passes through your kidneys and leaves as urine relatively quickly. What slows that process down is the presence of electrolytes (mainly sodium and potassium), protein, and a small amount of sugar. These nutrients signal your kidneys to retain more fluid rather than flushing it out.
This is exactly why milk performs so well. It contains sodium, potassium, protein, and a natural sugar called lactose, all in a combination that slows gastric emptying and encourages your intestines to absorb more water. In a study of children rehydrating after exercise in the heat, skim milk retained 74% of the fluid consumed after two hours. A carbohydrate-electrolyte sports drink retained 59%, and plain water only 47%.
How Common Drinks Actually Rank
The Beverage Hydration Index, developed by researchers at Loughborough University, measures how much fluid your body retains from a drink compared to water. A score of 1.0 means it hydrates the same as water. Anything above 1.0 means your body holds onto more fluid.
- Skim milk: 1.58
- Oral rehydration solution: 1.54
- Full-fat milk: 1.50
- Orange juice: roughly 1.3
- Cola: roughly 1.1
- Sports drink: roughly 1.1
- Coffee: 1.0
- Tea: 1.0
Sports drinks, despite heavy marketing, performed only slightly better than water. Coffee and tea, often blamed for dehydration, hydrated just as well as water in the amounts tested. The caffeine in those drinks didn’t cause meaningful fluid loss.
When You Need an Oral Rehydration Solution
Oral rehydration solutions are the gold standard for serious dehydration, especially from illness. The World Health Organization’s formula uses a precise balance of 75 mmol/L sodium and 75 mmol/L glucose. That one-to-one ratio matters because sodium and glucose are co-transported across your intestinal wall. When they arrive together, they pull water along with them far more efficiently than either one alone.
Commercial ORS products like Pedialyte and Drip Drop follow this principle. They’re your best option when you’re losing fluid rapidly from vomiting, diarrhea, or fever, situations where milk might not sit well in your stomach. If you can’t get to a store, you can make a basic version at home: 4 cups of water, half a teaspoon of table salt, and 2 tablespoons of sugar. This recipe, recommended by the University of Virginia School of Medicine, approximates the electrolyte balance of commercial solutions.
Rehydration After Exercise
For workouts under 60 minutes, plain water handles rehydration just fine. Your sweat losses at that duration are modest enough that food at your next meal replaces the electrolytes you’ve lost. Sports drinks become more useful once you’re exercising intensely for 60 minutes or longer, and they become important beyond 90 minutes, when sodium losses from sweat start to add up.
For very long efforts like marathons or ultramarathons lasting three to five hours or more, you need a drink with meaningful sodium content. Drinking only plain water during prolonged endurance exercise can actually be dangerous. A condition called exercise-associated hyponatremia occurs when excessive water intake dilutes the sodium in your blood below safe levels. It’s the most common cause of serious medical events at endurance races, and the primary driver is too much water without enough sodium to match.
Milk is an excellent post-exercise recovery drink but isn’t practical mid-workout for obvious reasons. After you’ve finished, though, its combination of protein, carbohydrates, and electrolytes makes it one of the most effective options for restoring fluid balance.
Coconut Water: A Middle Ground
Coconut water has earned a reputation as a natural sports drink, and it partly deserves it. One cup contains about 404 mg of potassium, more than ten times the 37 mg found in a cup of Gatorade. Potassium helps with cellular hydration and muscle function, making coconut water a solid choice for everyday rehydration and light exercise.
The catch is sodium. Coconut water provides only about 64 mg of sodium per cup, compared to 97 mg in the same amount of Gatorade. For heavy sweating, that sodium gap matters. Your sweat is primarily a sodium-based fluid, so replacing potassium alone won’t fully restore what you’ve lost. You can bridge this gap by adding a small pinch of salt to coconut water if you’re using it after a hard workout.
Picking the Right Drink for Your Situation
The “best” rehydration drink shifts based on context. For everyday hydration and mild dehydration, skim milk or full-fat milk outperforms everything else tested, assuming you tolerate dairy. For stomach illness with vomiting or diarrhea, an oral rehydration solution is the better choice because it’s gentle on the stomach and engineered for rapid absorption. For exercise under an hour, water is sufficient. For longer or more intense sessions, a sports drink or ORS with adequate sodium protects against both dehydration and dangerous sodium dilution.
One thing the research makes clear: you don’t need to spend much money on this. A homemade salt-and-sugar solution works nearly as well as commercial ORS. Milk from your fridge outperforms most products on the shelf. And for the vast majority of daily life, drinking water with your regular meals provides all the rehydration your body needs. The specialty drinks earn their place when fluid losses are heavy, rapid, or prolonged.