Water works for mild dehydration, but it’s not the most effective option. Drinks that contain small amounts of sodium, sugar, and protein are retained by your body significantly better than plain water, sometimes keeping 50% more fluid in your system over two hours. The best choice depends on how dehydrated you are and what caused it.
Why Water Alone Isn’t Always Enough
Your small intestine absorbs water fastest when sodium and glucose are present together. These two molecules are pulled into intestinal cells as a pair through a dedicated transport channel, and the movement creates a small osmotic gradient that draws water along with them, through and between cells. Plain water lacks this one-two punch, so it passes through more slowly and a larger share ends up as urine rather than staying in your bloodstream.
This is the principle behind every oral rehydration solution on the market, from Pedialyte to the packets used in hospitals worldwide. It’s also why a pinch of salt and a spoonful of sugar in water has saved millions of lives in regions without IV access.
The Best Drinks Ranked by Fluid Retention
A landmark study published in the American Journal of Clinical Nutrition developed a “Beverage Hydration Index” by measuring how much fluid people retained two hours after drinking various beverages, compared to still water. The results were striking:
- Skim milk retained the most fluid, with a hydration index of 1.58 (meaning 58% more fluid retained than water).
- Oral rehydration solutions scored 1.54.
- Full-fat milk scored 1.50.
- Orange juice also outperformed water at the two-hour mark.
- Sports drinks performed no differently than plain water at four hours. The extra urine output essentially cancelled out whatever the electrolytes provided.
Milk’s advantage comes from its protein content. About 80% of milk protein is casein, which empties from the stomach more slowly than carbohydrate-based drinks. That slower emptying gives your intestines more time to absorb the fluid. Research isolating the effect of milk protein found that even when fat and calorie content were matched, protein-containing solutions were better retained than carbohydrate-only solutions. The natural sodium, potassium, and lactose in milk help too.
Oral Rehydration Solutions
If you’re dealing with vomiting, diarrhea, or heat exhaustion, an oral rehydration solution (ORS) is the gold standard. The formula recommended by the World Health Organization since 2002 contains 75 millimoles per liter each of sodium and glucose, with a total concentration of 245 milliosmoles per kilogram. That precise balance maximizes the sodium-glucose cotransport mechanism without pulling extra water into the gut (which would make diarrhea worse).
Commercial versions include Pedialyte, DripDrop, and Liquid IV. They’re not identical in composition, so check the label. Products with very high sugar content work against you by increasing the osmotic load in your intestines.
A Simple Homemade Version
If you don’t have a commercial product on hand, the University of Virginia School of Medicine recommends this recipe: 4 cups of water, half a teaspoon of table salt, and 2 tablespoons of sugar. Stir until dissolved. It won’t taste great, but it closely mimics the electrolyte-to-sugar ratio your gut needs. Precision matters here. Too much sugar draws water into the intestines instead of absorbing it, and too much salt can worsen dehydration.
Coconut Water, Sports Drinks, and Juice
Coconut water is often marketed as nature’s sports drink, and it does have a useful electrolyte profile, just not the one most people assume. One cup contains about 404 mg of potassium but only 64 mg of sodium. By comparison, a cup of Gatorade has 97 mg of sodium and just 37 mg of potassium. If you’ve been sweating heavily, sodium is the electrolyte you’ve lost the most of, so coconut water alone won’t replace it efficiently. It’s a better fit for general daily hydration or mild dehydration where sodium loss isn’t the primary concern.
Sports drinks like Gatorade and Powerade are designed more for fueling exercise than for rehydrating after illness. Their sugar content is higher than what the WHO formula calls for, and as the hydration index study showed, they don’t actually help your body hold onto fluid any better than water over four hours. They’re fine during prolonged exercise when you need both carbohydrates and fluid, but they’re not the best recovery drink.
Orange juice performed well in the hydration index, likely because of its natural sugar, potassium, and calorie content. The downside is that its acidity can irritate your stomach if you’re already nauseous, and the fructose content can worsen diarrhea in some people.
How Quickly Different Drinks Are Absorbed
Not all fluids leave your stomach at the same rate. A study measuring gastric emptying found that a low-calorie fruit juice cleared the stomach in roughly 89 minutes on average, while higher-calorie and higher-fat drinks took considerably longer, up to 152 minutes for a higher-fat oat drink. Drinks with more calories, protein, or fat slow gastric emptying, which is a double-edged sword: slower emptying means better fluid retention, but it also means you won’t feel relief as quickly.
For rapid rehydration, something low in fat and moderate in sugar (like an ORS or diluted juice) will reach your intestines fastest. For sustained hydration over several hours, milk or a protein-containing drink keeps fluid in your system longer.
What to Drink for Specific Situations
Your best option shifts depending on the cause:
- After a stomach bug: Small, frequent sips of an oral rehydration solution. Avoid milk until vomiting stops, since fat and protein can trigger nausea. Start with a few tablespoons every 10 to 15 minutes and increase as tolerated.
- After heavy exercise or heat exposure: An ORS or skim milk. If you’ve been sweating for over an hour, you need sodium more than potassium, so coconut water alone won’t cut it.
- After a night of drinking alcohol: Water with electrolytes or a commercial ORS. Alcohol suppresses the hormone that tells your kidneys to retain water, so you’ve lost both fluid and sodium. A glass of milk before bed can help, since the protein slows absorption.
- General mild dehydration (headache, dark urine, dry mouth): Plain water is usually sufficient. Adding a small pinch of salt or drinking it alongside a meal speeds absorption.
Rehydrating Children
Children dehydrate faster than adults because of their higher surface-area-to-body-weight ratio. CDC guidelines recommend giving a child with mild to moderate dehydration 50 to 100 milliliters of oral rehydration solution per kilogram of body weight over two to four hours, plus extra to replace ongoing losses from vomiting or diarrhea. For a 20-pound (9 kg) child, that works out to roughly 15 to 30 ounces over a few hours.
Pedialyte or a similar pediatric ORS is the first choice. Avoid giving young children sports drinks, fruit juice, or soda. These have too much sugar relative to sodium and can actually pull water into the intestines, worsening diarrhea. For babies who are breastfeeding, continue nursing alongside the ORS.
When Drinking Isn’t Enough
Oral rehydration works for mild to moderate dehydration, but there’s a threshold where the body can’t recover without IV fluids. Moderate dehydration that isn’t improving with oral intake typically requires intravenous rehydration in an urgent care or emergency setting.
Signs that dehydration has become serious include confusion or slurred speech, a rapid pulse paired with low blood pressure, fainting or loss of consciousness, muscle twitching, and the inability to keep fluids down. In children, watch for no tears when crying, no wet diapers for three or more hours, and unusual drowsiness. A fever above 103°F alongside these symptoms points toward heatstroke, which is a medical emergency.