Water is the obvious first choice, but it’s not actually the most hydrating option. Research measuring how long fluids stay in your body (rather than passing through as urine) found that drinks containing electrolytes and a small amount of sugar outperform plain water by a significant margin. The best drink depends on how dehydrated you are and what caused it.
The Most Hydrating Drinks, Ranked
A study that created a Beverage Hydration Index, scoring drinks based on how much fluid your body retains over several hours, found that oral rehydration solutions scored highest at 1.50, followed by skim milk at 1.44 and full-fat milk at 1.32. Plain water served as the baseline at 1.0. The pattern is clear: drinks with higher levels of sodium and potassium keep fluid in your body longer instead of sending it straight to your kidneys.
This doesn’t mean you need to chug milk every time you’re thirsty. For mild dehydration from a hot day or a skipped water bottle, plain water works fine. But when you’ve lost significant fluid from vomiting, diarrhea, heavy exercise, or illness, reaching for something with electrolytes will restore your hydration faster and more completely.
Why Electrolytes Matter More Than Volume
Your gut absorbs fluid based on what’s dissolved in it. Drinks with a lower concentration of sugar and salt than your blood (called hypotonic drinks) get absorbed the fastest because water moves quickly across your intestinal wall into your bloodstream through osmosis. Drinks with very high sugar concentrations, above about 8%, actually pull water out of your bloodstream and into your intestine to dilute themselves before they can be absorbed. This is why chugging a sugary soda when you’re dehydrated can temporarily make things worse.
The sweet spot for absorption is a carbohydrate concentration between 1% and 4%. Solutions in that range move into your bloodstream faster than plain water. Go above that, and absorption slows down. Most oral rehydration solutions are designed around this principle, with about 3 to 4% carbohydrate and a relatively high sodium content.
Oral Rehydration Solutions vs. Sports Drinks
These two products look similar on the shelf but are built for different purposes. A typical oral rehydration solution contains roughly three times the sodium of a standard sports drink (about 61 millimoles per liter versus 18). It also has less sugar, around 3.4% carbohydrate compared to about 6% in a sports drink. Oral rehydration solutions are designed to replace what you lose during illness. Sports drinks are designed to fuel exercise while providing some hydration.
If you’re dehydrated from a stomach bug or food poisoning, an oral rehydration solution is the better choice. If you’re dehydrated from a long run or working outdoors, a sports drink will work, though diluting it slightly with water can improve absorption speed. For everyday mild dehydration, either one is more than you need, and water with a salty snack will do the job.
Coconut Water, Tea, and Coffee
Coconut water performs about as well as a sports drink for rehydration. A study comparing coconut water, a carbohydrate-electrolyte sports drink, and plain water found no meaningful differences in fluid retention or physical performance afterward. Coconut water is naturally high in potassium, which helps, though it’s lower in sodium than ideal for serious dehydration. It’s a solid option for mild to moderate cases.
Coffee and tea are fine despite their caffeine content. Caffeine is technically a diuretic, meaning it increases urine production. But the fluid in a cup of coffee or tea more than offsets this effect at normal consumption levels. High doses of caffeine taken all at once can increase urine output, especially if you don’t drink caffeine regularly, but your morning coffee isn’t dehydrating you.
What to Avoid
Alcohol is genuinely dehydrating. It suppresses the hormone that tells your kidneys to hold onto water, so you lose more fluid than you take in. Drinking alcohol while already dehydrated compounds the problem.
Sugary drinks like fruit juice, soda, and energy drinks with high sugar concentrations slow fluid absorption and can worsen diarrhea by drawing water into the intestine. Many doctors still recommend “clear liquids” like apple juice or ginger ale for stomach illness, but these often contain too much sugar and too little sodium to effectively rehydrate. They can actually increase stool output and create electrolyte imbalances.
How Much and How Fast to Drink
If you’re mildly dehydrated, sipping steadily is more effective than gulping a large volume at once. Your intestine can only absorb fluid so fast, and drinking too quickly can trigger nausea, especially if you’re already feeling sick. For adults, aiming for about 200 to 300 milliliters (roughly a cup) every 15 to 20 minutes is a reasonable pace until you feel better.
For children, the approach is more cautious. Small, frequent sips work best: about a teaspoon (5 mL) every two minutes. A commonly used guideline is 50 to 100 mL per kilogram of body weight over two to four hours. So a 10-kilogram toddler (about 22 pounds) would need roughly 500 mL to 1 liter over that window. After each episode of watery stool, adding about 10 mL per kilogram of body weight helps keep up with ongoing losses.
Infants are at higher risk of dehydration than older children or adults. They have a higher metabolic rate relative to their size, lose more water through their skin, and obviously can’t get their own fluids. Oral rehydration solutions are safe for any age, but infants who can’t keep fluids down or who seem lethargic need medical attention quickly.
Signs That Drinking Isn’t Enough
Most dehydration resolves with oral fluids. But severe dehydration, where someone is confused, has a rapid heartbeat, produces little or no urine, or can’t keep fluids down due to persistent vomiting, requires intravenous fluids. The same applies if someone is in or near shock, with cold extremities, rapid breathing, or extreme lethargy. In these situations, the gut can’t absorb fluid fast enough to match what’s being lost, and IV treatment is the only way to catch up.
A Simple Homemade Rehydration Drink
If you don’t have a commercial oral rehydration solution available, you can approximate one with six teaspoons of sugar and half a teaspoon of salt dissolved in a liter of clean water. This gives you roughly the right concentration of glucose and sodium to speed absorption. It won’t taste great, but it works. Adding a splash of orange juice or a squeeze of lemon can improve the flavor and add a small amount of potassium.