What Beverage Hydrates You the Most? The Surprising Science of Superior Hydration

December 15, 2025 •

4 min read

According to a 2016 study from Scotland's St. Andrews University that developed the 'Beverage Hydration Index' (BHI), plain water isn't always the most effective at hydrating the body over a longer period. For those wondering what beverage hydrates you the most, the answer might surprise you and is rooted in the beverage's composition.

Quick Summary

Scientific studies reveal that drinks containing electrolytes, proteins, and carbohydrates, such as milk and oral rehydration solutions, provide more effective and longer-lasting hydration than water alone.

Key Points

Surprising Top Ranker: Studies show milk, particularly skim milk, is often more hydrating than water over time due to its nutrient content.
The Power of Electrolytes: Oral Rehydration Solutions (ORS) and milk contain electrolytes like sodium and potassium, which help the body retain fluids.
It's About Retention: Plain water hydrates quickly but is excreted faster than beverages with a mix of electrolytes and nutrients.
Hydration from Food: A significant portion of your daily fluid intake comes from high-water content foods like fruits and vegetables.
Personalized Needs: The ideal beverage depends on your activity level, climate, and overall health status, so there's no single best choice.
Check the Sugar: Highly sugary drinks like soda and some juices are less effective for hydration and can lead to osmotic water loss.
Moderate Caffeine is OK: Contrary to popular myth, moderate consumption of coffee and tea does not significantly dehydrate you and contributes to fluid intake.

The Science Behind Hydration: More Than Just Water

Hydration is a complex process. When you drink a beverage, its fluid is absorbed into the bloodstream. However, how long that fluid stays in your body, and how effectively it is utilized, depends on more than just its water content. The presence of electrolytes like sodium and potassium, as well as nutrients like carbohydrates and protein, influences a process called gastric emptying, where fluid exits the stomach. Slower gastric emptying means the body can absorb the fluid over a longer duration, leading to superior, sustained hydration.

The Role of Electrolytes and Nutrients

Electrolytes: Sodium, potassium, and other electrolytes are vital for managing fluid balance within your body's cells. When you sweat heavily, you lose these minerals along with water. Replenishing them is key to effective rehydration.
Carbohydrates: The sugar (glucose) in some beverages works with sodium to enhance water absorption in the small intestine via sodium-glucose cotransporters. This process is crucial for rapid and efficient fluid uptake.
Protein and Fat: These macronutrients slow down the rate at which fluid leaves the stomach. This prolonged retention period allows the body to absorb the fluid more effectively over time, reducing immediate urine output.

The Contenders: Ranking the Most Hydrating Beverages

Milk: The Unexpected Champion

Numerous studies, including the seminal 2016 St. Andrews research, consistently rank skim and full-fat milk higher than water on the Beverage Hydration Index. This is due to its impressive nutritional profile: a combination of high water content, natural sugars (lactose), protein, fat, and critical electrolytes like sodium and potassium. For post-exercise recovery, milk has been shown to be particularly effective at restoring fluid balance. The protein content also helps with tissue repair, making it a powerful recovery beverage for athletes and anyone recovering from a strenuous activity.

Oral Rehydration Solutions (ORS): For Intensive Hydration

For serious dehydration, especially from illness like diarrhea or vomiting, Oral Rehydration Solutions (ORS) are scientifically formulated to be highly effective. ORS contains a precise balance of water, glucose, sodium, and potassium to optimize fluid absorption in the intestines. This makes them superior to plain water when significant fluid and electrolyte loss has occurred. While ORS is a lifesaver in severe cases, it's also highly effective for athletes experiencing intense, prolonged sweat loss.

Beyond the Top Two: Other Excellent Choices

While milk and ORS may take the top spots for sustained rehydration, other beverages also contribute significantly to your fluid intake:

Coconut Water: Naturally rich in electrolytes, particularly potassium, coconut water is a refreshing and beneficial hydrator. Look for options without added sugar.
Broth-Based Soups: Warm broth is not only soothing but also contains water and electrolytes like sodium and potassium, which aid in rehydration, especially during illness.
Infused Water and Herbal Tea: If you find plain water boring, adding fresh fruit like lemon, cucumber, or berries can make it more palatable. Caffeine-free herbal teas also provide fluid and often contain antioxidants without the diuretic effect of higher caffeine drinks.
High-Water Content Foods: Don't overlook solid foods. Fruits like watermelon (92% water) and strawberries (91%), along with vegetables like cucumbers (97%) and lettuce (96%), provide a significant portion of your daily fluid intake.

Drinks That Are Not Your Best Hydration Bet

Not all beverages are created equal when it comes to hydration. Those high in concentrated sugars, like sodas and many fruit juices, can actually pull water from your body into the intestine to dilute the sugar load, a process called osmosis. This makes them less hydrating and adds unnecessary calories. Additionally, while moderate caffeine intake won't dehydrate you, excessive amounts can have a mild diuretic effect. Strong alcoholic drinks are notably dehydrating, as alcohol is a diuretic that increases urine production.

Hydrating for Your Needs: A Comparison Table


Beverage	Primary Hydration Mechanism	Best For	Considerations	BHI Score*
Skim Milk	Electrolytes, protein, and natural sugars slow gastric emptying, retaining fluid longer.	Sustained hydration, post-exercise recovery, replacing lost electrolytes.	Calorie content, potential for lactose intolerance.	~1.58
Oral Rehydration Solution (ORS)	Precise balance of sodium and glucose maximizes intestinal water absorption.	Replenishing fluids after illness (diarrhea, vomiting) or intense, prolonged exercise.	Higher cost than homemade alternatives.	~1.54
Plain Water	High water content is absorbed quickly.	Daily, general hydration; most situations for the average person.	Offers fast hydration but is excreted more quickly than milk/ORS.	1.00 (Baseline)
Coconut Water	Natural electrolytes like potassium aid in fluid balance.	Light hydration during moderate activity or to replenish minerals.	Check for added sugars; can cause bloating in some.	Lower than Milk/ORS
Sports Drink	Electrolytes and carbohydrates.	Replenishing fluid and fuel during intense exercise lasting over an hour.	Often high in sugar and calories; not necessary for general hydration.	Close to Water

*Note: BHI scores vary by study methodology. These are representative of findings from the St. Andrews study.

Conclusion: Tailoring Your Hydration Strategy

While water remains the most accessible and fundamental option for daily hydration, scientific studies reveal that it's not the most effective at long-term fluid retention. For superior, sustained hydration—especially after significant fluid loss—milk and oral rehydration solutions excel due to their electrolyte and nutrient content. By understanding the mechanisms at play, you can make more informed choices, whether you are rehydrating after intense exercise, battling an illness, or simply trying to stay adequately hydrated throughout the day. Remember to consider your specific needs, activity levels, and personal health to optimize your fluid intake. For general health, a varied approach incorporating plain water, water-rich foods, and other beneficial beverages is the most effective strategy. To dive deeper into the science, see the detailed explanation behind the hydration index: The Hydration Index | ProSource - ACE Fitness.

Frequently Asked Questions

Yes, plain water is the gold standard for daily, general hydration needs, as it is calorie-free and effective for most situations. For short-term fluid replenishment, it works quickly.

Milk is more hydrating over time because its combination of natural sugars (lactose), protein, fat, and electrolytes slows gastric emptying, allowing the body to absorb and retain fluids for longer.

Sports drinks are designed for intense, prolonged exercise lasting over an hour to replace carbohydrates and electrolytes lost through sweat. For moderate activity, water is sufficient, as sports drinks often contain high amounts of sugar.

No, not in moderation. While caffeine is a mild diuretic, the fluid volume in coffee and tea is enough to offset this effect, and it still contributes to your overall hydration.

Common signs of dehydration include thirst, dark yellow urine, fatigue, a dry mouth, and infrequent urination. Checking your urine color is a good rule of thumb, aiming for a pale yellow shade.

Yes, approximately 20% of your daily fluid intake comes from water-rich foods like fruits and vegetables, so incorporating them into your diet can significantly boost your hydration.

An ORS is used for intensive hydration, typically to treat dehydration caused by illness (like diarrhea or vomiting) or significant fluid loss from extreme exercise, as it contains an optimal balance of electrolytes and glucose.

While rare, it is possible to overhydrate, a condition called hyponatremia, which occurs when sodium levels in the body become dangerously diluted. This is mainly a risk for endurance athletes or individuals with certain medical conditions.