Water is the obvious answer, but it’s not the only good one, and it’s not even the best. Research measuring how long fluids stay in your body found that milk, orange juice, and oral rehydration solutions all outperform plain water for hydration. Coffee, tea, sparkling water, and even cola hydrate about as well as still water. The real question isn’t just what you drink but what’s in it that helps your body hold onto fluid.
Why Milk Outperforms Water
A landmark study created what’s called the Beverage Hydration Index, scoring drinks against still water (set at 1.0) based on how much fluid your body retains over several hours. Skim milk scored 1.58, full-fat milk scored 1.50, and orange juice came in at 1.39. After adjusting for water content, both types of milk and oral rehydration solutions remained significantly better than water at keeping you hydrated.
The reason comes down to what else is in the glass. Milk contains naturally high concentrations of sodium and potassium, two minerals your kidneys use to regulate fluid balance. When those minerals are present, your kidneys reabsorb more water instead of sending it to your bladder. Milk also has carbohydrates, protein, and fat, which slow down how quickly liquid empties from your stomach. That slower release gives your intestines more time to absorb the fluid. The trade-off: drinking large amounts of milk during or after heavy sweating can cause bloating and stomach discomfort, so it works better as a steady hydration source throughout the day than as a rapid recovery drink.
Sports Drinks, Coconut Water, and Electrolytes
Sports drinks are designed to replace what you lose in sweat, but they didn’t score significantly better than water in the Beverage Hydration Index. That doesn’t mean they’re useless. During prolonged exercise (roughly 60 minutes or more), the sodium in sports drinks helps your body absorb water faster and replace what’s lost through sweat. A 16-ounce serving of Gatorade contains about 160 mg of sodium and 45 mg of potassium. Powerade is similar, with 150 mg of sodium and 35 mg of potassium.
Coconut water takes a different approach. It’s packed with potassium (404 mg per cup versus 37 mg in a cup of Gatorade) but contains less sodium (64 mg versus 97 mg). That makes it a solid everyday hydration choice, but less ideal for heavy exercise recovery, where sodium replacement matters most. If you’re just looking for something more interesting than water during a normal day, coconut water is a strong option.
Coffee and Tea Count
The idea that coffee dehydrates you is one of the most persistent hydration myths. In the Beverage Hydration Index study, hot tea, iced tea, and coffee all produced the same fluid retention as water. None of the caffeinated beverages tested had a lower hydration score.
Caffeine does act as a mild diuretic, but the dose matters enormously. Research published in Frontiers in Nutrition found that caffeine at about 3 mg per kilogram of body weight (roughly two to three cups of coffee for most adults) doesn’t disrupt fluid balance at all. The diuretic effect only kicks in at around 6 mg per kilogram, which works out to roughly four or more cups. So your morning coffee or afternoon tea is contributing to your daily fluid intake, not working against it.
What About Soda and Sugary Drinks?
Regular cola and diet cola both hydrated as well as water in the Beverage Hydration Index, which might seem surprising. But there’s a catch worth understanding. Drinks with very high sugar concentrations can actually pull water into your intestines rather than letting your body absorb it. This happens because your gut tries to dilute the concentrated sugar, drawing fluid from surrounding tissues into the intestinal tract. The result can be bloating, cramping, and diarrhea, all of which work against hydration.
The colas tested in the study have moderate sugar levels. Fruit juices, energy drinks, and sodas with higher sugar content may behave differently, especially if you drink them quickly on an empty stomach. As a general rule, drinks with some sugar help your body absorb water (this is the principle behind oral rehydration solutions), but too much sugar reverses that benefit.
Sparkling Water Works Just as Well
If you prefer carbonated water, there’s no reason to switch. Research shows no significant difference in fluid retention or urine output between sparkling and still water. The carbonation doesn’t interfere with absorption. Some people find the fizz makes them drink more throughout the day, which is a net positive for hydration. The only consideration is that carbonation can cause mild bloating in some people, but it won’t change how well the water hydrates you.
Alcohol Is the Exception
Alcohol is the one common drink category that works against hydration. It suppresses the hormone that tells your kidneys to retain water, which is why you urinate more frequently when drinking. Research hasn’t pinpointed an exact alcohol percentage where a drink flips from hydrating to dehydrating, but the general pattern is clear: the higher the alcohol content, the more fluid you lose. Beer (tested as lager in the Beverage Hydration Index) performed about the same as water, likely because its alcohol content is low enough that the fluid volume compensates. Spirits and wine are a different story.
How Much Fluid You Actually Need
The National Academies of Sciences recommends a total daily water intake of about 3.7 liters (131 ounces) for men and 2.7 liters (95 ounces) for women ages 19 to 30. That sounds like a lot, but roughly 19 percent of your daily water comes from food, especially fruits, vegetables, soups, and yogurt. That leaves men needing about 3 liters from drinks and women about 2.2 liters.
These numbers are averages. You’ll need more if you exercise, live in a hot climate, are pregnant or breastfeeding, or are recovering from illness. The simplest way to check your hydration: urine color. Pale yellow means you’re well hydrated. Dark yellow or amber means you need more fluids.
Practical Hydration Rankings
Based on the research, here’s how common drinks stack up for keeping you hydrated:
- Better than water: Skim milk, full-fat milk, oral rehydration solutions
- Equal to water: Orange juice, sparkling water, coffee, tea (hot and iced), cola, diet cola, sports drinks, beer (low ABV)
- Worse than water: Drinks with very high sugar content consumed in large amounts, wine, spirits
The best hydration strategy isn’t about finding one perfect drink. It’s about getting enough total fluid from a variety of sources throughout the day. Water is a reliable baseline, milk and coconut water add electrolytes naturally, and your daily coffee is doing more good than you probably thought.