Understanding the Science: Which drinks hydrate the best?

November 2, 2025 •

4 min read

While water is often considered the gold standard for hydration, a study from Scotland's St. Andrews University revealed that beverages with a small amount of sugar, fat, or protein might keep you hydrated for longer. This discovery challenges conventional wisdom and prompts a deeper look into which drinks hydrate the best for different situations, from daily wellness to post-workout recovery.

Quick Summary

This article explores the science of hydration, detailing how certain beverages like milk and oral rehydration solutions can be more effective than plain water. It examines the role of electrolytes and macronutrients in fluid absorption and offers guidance on optimal drink choices for daily life, athletic performance, and recovery from illness.

Key Points

Electrolytes are Key: Drinks containing electrolytes like sodium and potassium, such as milk and ORS, are more hydrating than plain water over a sustained period.
Milk is a Surprising Contender: Milk’s combination of protein, fat, and lactose helps slow gastric emptying, allowing for more prolonged fluid absorption and greater hydration than water.
Water is the Daily Standard: For general, everyday hydration, calorie-free water remains the most accessible and healthy choice.
Context is Crucial: Choose your drink based on your activity and state. Use water for daily sipping, sports drinks for intense exercise, and ORS for illness-related dehydration.
Monitor Your Status: Check your hydration level by observing urine color (pale yellow is ideal) and the skin turgor test.
Foods Can Hydrate, Too: Water-rich foods like watermelon, cucumber, and soups can contribute significantly to your daily fluid intake.

The Science Behind Hydration

Proper hydration is critical for nearly every bodily function, including regulating body temperature, lubricating joints, and transporting nutrients. However, the effectiveness of a hydrating drink isn't just about its water content. It's also influenced by its nutrient composition, which affects how quickly the liquid is absorbed and how long it stays in the body.

The Beverage Hydration Index (BHI)

In 2016, a study published in the American Journal of Clinical Nutrition introduced the Beverage Hydration Index (BHI) to compare the short-term hydration potential of different drinks relative to still water. Researchers found that certain beverages, like milk and oral rehydration solutions (ORS), resulted in less urine output and a higher net fluid balance than plain water over several hours. This is because electrolytes like sodium and potassium, along with nutrients like protein and carbohydrates, slow down the process of gastric emptying and improve fluid absorption in the intestines.

Top Hydrating Drinks and Their Benefits

Oral Rehydration Solutions (ORS)

For rapid and effective rehydration, especially during illness involving fluid loss from vomiting or diarrhea, ORS are a top choice. They contain a specific balance of water, glucose, and electrolytes (sodium and potassium) that maximizes fluid absorption in the gastrointestinal tract through a sodium-glucose co-transport system. This is why they are often used in medical settings to prevent and treat dehydration.

Milk

Surprisingly, milk (both skim and full-fat) has been shown to be more hydrating than water over a four-hour period. The secret lies in its composition of lactose (sugar), protein, and fat. These macronutrients help slow the emptying of fluid from the stomach, which allows for a more sustained and effective hydration process. Milk's natural sodium content also helps the body retain water, leading to less urine production.

Water

Plain water remains the best, most accessible option for everyday hydration. It is calorie-free and effectively replenishes lost fluids for most people in most situations. For short, low-intensity activities, water is all that is needed to maintain good hydration. However, in conditions of heavy sweating or illness, it's not the most efficient choice for replacing lost electrolytes.

Coconut Water

Naturally rich in electrolytes like potassium, coconut water is a popular choice for rehydration, particularly after light exercise. It contains natural sugars and electrolytes but typically has lower sodium levels compared to sports drinks, making it a better option for general replenishment rather than intense endurance activities.

Sports Drinks

Formulated with electrolytes and carbohydrates, sports drinks are designed to replenish fluids, salts, and energy during high-intensity or prolonged exercise lasting more than 60 minutes. The carbohydrates aid in electrolyte absorption and provide fuel for muscles. However, their high sugar content makes them unnecessary for everyday hydration and potentially counterproductive due to extra calories.

Comparison of Hydrating Drinks


Drink	Effectiveness	Key Nutrients	Best For...	Considerations
Oral Rehydration Solution (ORS)	Very High	Sodium, Glucose, Potassium	Illness (vomiting, diarrhea), severe dehydration	High effectiveness, often unpalatable taste
Milk	High	Protein, Fat, Lactose, Sodium, Potassium	Post-exercise recovery, prolonged hydration	Contains calories, lactose may be an issue for some
Water	Standard	-	Everyday hydration, low-intensity exercise	Most accessible, calorie-free, doesn't replace lost electrolytes during heavy sweat
Coconut Water	Good	Potassium, Magnesium, Calcium	General wellness, light exercise	Lower in sodium, check labels for added sugars
Sports Drinks	Good (Situational)	Electrolytes, Carbohydrates	High-intensity, long-duration exercise	Often high in added sugar, not for daily use
Fruit Juices	Moderate	Water, Vitamins, Natural Sugars	Limited use alongside other fluids	High in sugar, can slow absorption due to osmosis

Signs of Good Hydration

The easiest way to know if you are sufficiently hydrated is to monitor your urine color. The goal is a pale yellow, similar to lemonade. Darker urine suggests you need more fluids, while consistently clear urine may indicate overhydration. Another quick way to check is the skin turgor test: pinch the skin on the back of your hand. If it snaps back quickly, you're hydrated; if it stays 'tented' for a moment, you need more fluids.

How to Choose Your Optimal Hydration Strategy

Choosing the best drink depends on your specific needs. For daily, all-purpose hydration, water is the ideal choice due to its lack of calories and additives. During and after intense exercise, particularly in hot conditions, a sports drink or coconut water can be beneficial to replace lost electrolytes and fuel. For recovery from illness, an ORS provides the most efficient rehydration.

Hydration during illness

When experiencing vomiting or diarrhea, your body loses significant fluids and electrolytes. An ORS is specifically formulated to replenish these losses quickly and effectively, making it the superior choice over plain water in these situations. For children and the elderly, who are more susceptible to rapid dehydration, ORS can be particularly life-saving.

Tips for better hydration

Stay ahead of thirst: Feeling thirsty is a sign that you are already mildly dehydrated. Sip fluids consistently throughout the day.
Enhance water flavor: Add slices of fruit like lemon, cucumber, or berries to your water to make it more appealing.
Eat your water: Water-rich foods like watermelon, cucumber, strawberries, and soups contribute significantly to your daily fluid intake.
Choose wisely: Be mindful of drinks high in added sugar, as they can contribute excess calories and potentially hinder efficient hydration.

For more information on nutrition, the Academy of Nutrition and Dietetics is a reliable resource (https://www.eatright.org/).

Conclusion

While water is the best daily choice for its accessibility and purity, it is not always the most effective hydrating drink in every scenario. Understanding the science of fluid absorption, driven by electrolytes and macronutrients, reveals why options like milk and Oral Rehydration Solutions are superior for long-lasting hydration and rapid recovery. By considering your personal needs, whether for everyday wellness or intensive activity, you can make informed choices to optimize your fluid intake and overall health.

Frequently Asked Questions

Yes, several studies indicate that both full-fat and skim milk are more hydrating than plain water over a four-hour period. This is because the protein, fat, and natural sugars in milk slow digestion and fluid release, helping the body retain fluids for longer.

You should choose an electrolyte drink during or after prolonged, high-intensity exercise (over 60 minutes), especially in hot weather, or when recovering from illness that causes fluid loss like vomiting or diarrhea. For general daily needs, water is sufficient.

Yes, many natural sources provide electrolytes. Coconut water is rich in potassium, while bone broth is high in sodium. Watermelon, oranges, bananas, and other fruits and vegetables also offer good amounts of electrolytes.

Oral Rehydration Solutions (ORS) are the most effective for rapid rehydration after illness involving fluid loss. They are formulated with a specific ratio of electrolytes and glucose to maximize quick absorption in the intestines.

While caffeine has a mild diuretic effect, moderate consumption of coffee and tea does not lead to dehydration. The fluid in the beverage is typically enough to offset any diuretic effects. However, excessive consumption can be dehydrating for some people.

The easiest way to check is to monitor your urine color; it should be a pale yellow. Darker urine suggests you need more fluid. You can also perform a skin turgor test by pinching the skin on the back of your hand—it should snap back quickly if you are hydrated.

No, drinks with high concentrations of sugar, like many fruit juices and sodas, can draw water out of the body and into the intestine through osmosis, potentially hindering effective hydration. They also contribute unnecessary calories and added sugars.