What Are the Most Hydrating Drinks? Ranked by Science
Scientists ranked 13 drinks by how well they actually hydrate, and plain water finished mid-pack. Here is the full ranking, why milk beat water, and what to drink.
What Are the Most Hydrating Drinks? Ranked by Science
Ask almost anyone what the most hydrating drink is and the answer comes back instantly: water. It is the default, the gold standard, the thing every health article tells you to drink more of. So it surprises people to learn that when researchers actually measured how well different drinks hydrate the body, plain water finished somewhere in the middle of the pack. A few common beverages held fluid in the body noticeably better, and one of the winners was not a sports drink or a fancy electrolyte powder. It was milk.
This is not a trick of marketing or a single cherry-picked study. It comes from a careful piece of research that built something called the Beverage Hydration Index, a way to rank drinks by how much fluid your body still retains a few hours after you drink them. The results are genuinely useful, because "hydration" is not just about how much liquid goes in. It is about how much stays in.
This article walks through how the ranking was actually measured, where every common drink lands, why milk and oral rehydration solutions beat plain water, where water still deserves to be your default, and how to turn all of this into a practical way of thinking about what is in your glass.
How Scientists Actually Measure Hydration
The intuitive idea of hydration is simple: drink fluid, get hydrated. The reality is more interesting. When you drink a large volume of plain water quickly, a surprising amount of it passes straight through and leaves as urine within an hour or two. Your kidneys sense the sudden dilution of your blood and dump the excess. So the fluid technically went in, but a lot of it did not stay.
Researchers at the University of St Andrews in Scotland set out to quantify this. They had volunteers drink one liter of a given beverage, then measured urine output over the next four hours and compared it to still water. From that they built the Beverage Hydration Index, or BHI, where still water is the baseline and scores a 1.0. A drink that keeps more fluid in the body than water scores above 1.0. A drink that holds less scores below it.
The single most important factor that emerged was not magic ingredients. It was two things working together: the electrolyte content of the drink, especially sodium, and the rate at which it leaves your stomach. Drinks with some sodium, some sugar, or some protein and fat empty from the stomach more slowly and trigger less of that "flush it out" kidney response. They hydrate more gradually and more completely. Plain water, with nothing in it, is absorbed fast and flushed fast.
The Ranking: Most Hydrating Drinks, Best to Worst
Here is roughly how common beverages landed, from the most fluid-retaining to the least. Treat the numbers as approximate, because individual bodies vary, but the order is robust.
Oral rehydration solution (around 1.5): The clinical rehydration drinks used for illness, with a precise ratio of sodium, potassium, and glucose, topped or nearly topped the chart. This is no accident. The formula is engineered specifically to maximize fluid retention.
Milk, skim and full-fat (around 1.5): This is the surprise. Both skim and whole milk held fluid in the body far better than water. Skim milk slightly edged out full-fat in some measures. The combination of natural sugars (lactose), sodium, potassium, protein, and fat is close to an accidental rehydration formula.
Orange juice (around 1.3 to 1.4): Fruit juice scored well, though some of that advantage shrinks once you account for the water already in the juice. Still, the sugar and small mineral content slow absorption and help retention.
Cola and diet cola (around 1.3): Surprising to many, regular and diet cola both scored above water. The sugar in regular cola and the small sodium content in both contribute. This does not make cola a health drink, for reasons we will get to, but on the narrow question of fluid retention, it does hold up.
Cold tea and sports drinks (around 1.1 to 1.3): These edged above water but, in the original research, not by a statistically convincing margin. They are roughly water-equivalent for hydration, with sports drinks earning their place during long, sweaty exercise for the sodium specifically, as the piece on electrolytes 101 explains.
Still water, sparkling water, hot tea, coffee, and beer (around 1.0): This is the broad middle. Plain water sets the baseline. Sparkling water hydrates essentially the same as still water, a point the sparkling versus still water article covers in detail. Coffee and tea, despite their caffeine reputation, land right around water too. And yes, even a light beer hydrates roughly like water in modest amounts, though alcohol's bigger picture is not friendly, as covered in alcohol and hydration.
The headline that "water doesn't win" is true, but it needs the asterisk that follows.
Why Milk Beats Water
Milk topping a hydration chart sounds like a contradiction, but the mechanism is straightforward once you see it.
Sodium and potassium. Milk naturally contains both. Sodium in particular signals your body to hold onto fluid rather than excrete it. This is the same principle behind oral rehydration solutions and behind the old advice to add a pinch of salt to water during heavy sweating.
Sugar (lactose). The natural sugar in milk slows gastric emptying. Fluid that leaves the stomach gradually is absorbed gradually, which avoids the rapid blood dilution that triggers urine production.
Protein and fat. Milk's protein and fat slow stomach emptying even further, extending the window over which the fluid is absorbed. This is why full-fat and skim milk both perform well, with only small differences between them.
The result is a drink that your body absorbs slowly and holds onto. It behaves, almost by accident, like a mild rehydration solution with calories and nutrition attached. This does not mean you should replace water with milk all day, but it does explain why a glass of milk is a legitimately good rehydration choice after exercise, and why it works as well as it does.
Where Plain Water Still Wins
If milk and cola beat water on the retention index, why is water still the right default? Because hydration efficiency per liter is only one of several things that matter, and on the others, water wins easily.
Zero calories. A liter of milk carries roughly 400 to 600 calories. A liter of cola or juice carries close to 400 calories of sugar. If you tried to meet your daily fluid needs through high-BHI drinks, you would consume a large part of your daily energy intake in liquid form. Water lets you hydrate freely without touching your calorie budget, which matters if you are tracking intake or managing weight.
No sugar load. Cola scoring above water on fluid retention does not make it a smart everyday drink. The sugar that helps it retain fluid also spikes blood sugar and feeds other health problems. Hydration is one metric; total health is another.
Cost and availability. Water is nearly free and available almost everywhere. No other drink on the list comes close on practicality.
It is what your body is mostly made of. For the steady, all-day maintenance hydration that the daily water intake guide is built around, plain water is exactly right. The BHI advantage of milk and ORS matters most in specific moments: after illness, after hard exercise, after heavy sweating. It matters much less for routine sipping through a normal day.
The honest takeaway is not "stop drinking water." It is "water is the right default, and a few other drinks are better tools for specific rehydration moments."
Drinks That Hydrate Less Than You Think
The index also clarifies a few drinks that people overrate or underrate.
Strong alcohol. Light beer hydrates roughly like water, but spirits and wine tip the balance the other way. Alcohol suppresses a hormone that tells your kidneys to conserve water, so stronger drinks make you lose more fluid than they provide. The alcohol and hydration and hangover prevention pieces cover why.
Coffee, but in context. A single coffee is mildly diuretic, but the fluid it contains more than offsets the small loss, so it lands near water on net. The persistent belief that coffee dehydrates you is mostly a myth, as the does coffee dehydrate you article details. The caveat is dose: several strong coffees in a row behave differently than one.
Sports drinks, outside of sport. Sports drinks earn their sodium during long, hot, heavy exercise. For a person sitting at a desk, they are sugar water with no advantage over plain water and a calorie cost. Context is everything.
A Practical Hydration Ranking for Real Life
Translating the science into daily decisions looks like this.
Your everyday default: plain water, still or sparkling, your choice. Free, calorie-free, endlessly available. This should be the bulk of your fluid.
After hard exercise or heavy sweating: milk, an oral rehydration drink, or water with electrolytes. This is where the high-BHI drinks earn their place, replacing both fluid and the sodium you lost. The athlete rehydration piece covers the sodium math.
Recovering from illness: an oral rehydration solution for anything significant, especially with vomiting or diarrhea. Milk or diluted juice can help with mild cases, but a proper ORS is the tool for real fluid loss.
For flavor and variety: tea, coffee in moderation, fruit-infused water, and milk all count toward your total. Hydration does not have to be plain water exclusively. Whole foods count too, as the hydrating foods article shows that water-rich fruits and vegetables contribute meaningfully.
When you want fluid without calories: plain or sparkling water, unsweetened tea, or black coffee. High retention is not the goal here; calorie-free hydration is.
Why Tracking Helps Here
The Beverage Hydration Index is a useful corrective to the "only water counts" myth, but it can also send people in the wrong direction if they over-index on it. The point is not to chase the highest-retention drink at every moment. It is to hit your total daily fluid target with drinks that fit the situation, and most of the time, that target is met with plain water plus whatever else you happen to drink.
This is exactly where logging helps. When you track your intake, milk, tea, coffee, and juice all count toward your total, not just water from the tap. A tracking app like Water Tracker lets you see your real daily fluid number rather than guessing, and it stops the common mistake of either undercounting (ignoring everything but water) or overcounting (assuming a single liter of cola is the same as a liter of water for your overall health). If you also use electrolyte supplements during heavy training, keeping those visible in a companion app like Supplements Tracker helps you see whether your sodium and potassium intake actually matches what your training demands, rather than guessing.
Conclusion
Water not winning the hydration race is a fun headline, but the real lesson is more practical. Hydration is about retention, not just volume, and drinks with a little sodium, sugar, protein, or fat hold fluid in the body better than plain water does. Milk and oral rehydration solutions sit at the top of the Beverage Hydration Index precisely because their composition slows absorption and signals your body to keep the fluid.
That does not dethrone water. Water remains the right everyday default because it hydrates well, costs nothing, carries no calories, and is always available. The smarter framing is to match the drink to the moment: plain water for routine sipping, milk or an oral rehydration solution after hard exercise or illness, and everything else counted honestly toward your daily total. The only number that ultimately matters is whether your total fluid intake lands where it should, and the best drink is the one that gets you there for the situation you are actually in.
Further reading
Disclaimer: This article is for informational purposes only and does not constitute medical advice. Consult a healthcare professional for personalized guidance.
