Beyond H2O: What is the most hydrating drink you can drink?

November 3, 2025 •

4 min read

According to a study published in The American Journal of Clinical Nutrition, drinks containing electrolytes, sugar, and protein can be even more hydrating than plain water. The simple question, 'What is the most hydrating drink you can drink?' has a surprising, science-backed answer that depends on your specific hydration needs and the electrolytes lost.

Quick Summary

This article explores the science of hydration, revealing that milk and Oral Rehydration Solutions (ORS) have a higher fluid retention index than water. It compares various beverages, explains the role of electrolytes, and offers practical advice for optimal hydration.

Key Points

Milk & ORS Often Outperform Water: Studies show skim milk and Oral Rehydration Solutions (ORS) often have a higher Beverage Hydration Index (BHI) than plain water, meaning the body retains their fluid longer.
Electrolytes are Key: Electrolytes like sodium and potassium help the body absorb and retain fluids, regulating balance inside and outside cells. Milk and ORS are rich in these minerals.
Hydration Depends on Context: Plain water is perfect for daily needs, but for rehydrating after intense exercise or illness, a drink with electrolytes and other nutrients, like milk or ORS, is more effective.
Fruits and Vegetables Also Hydrate: Up to 20% of your daily fluid intake can come from water-rich foods like watermelon, strawberries, cucumbers, and leafy greens.
Moderate Caffeine Intake is Fine: Moderate consumption of caffeinated drinks like coffee and tea does not lead to dehydration; the hydrating effect of the water typically outweighs the mild diuretic effect.
Flavor Improves Intake: Adding fruit or herbs to water can make it more palatable, encouraging increased fluid intake throughout the day.

The Surprising Science of Hydration

For years, water has been crowned the undisputed champion of hydration. While it remains a fundamental component of good health, scientific research has introduced a nuance to this common wisdom. The concept of a "Beverage Hydration Index" (BHI), developed by a team of researchers at St. Andrews University in Scotland, reveals that certain drinks can be more effective at fluid retention over a sustained period than plain water.

The key lies in the fluid's composition. Beverages containing electrolytes, a small amount of sugar, and sometimes protein and fat, can be absorbed more slowly and retained longer by the body. This is because these components slow the emptying of fluid from the stomach and assist the body's cells in absorbing water more efficiently. Electrolytes like sodium and potassium are particularly crucial, acting like sponges that help hold water in the body and balance fluid inside and outside the cells.

The Candidates for Most Hydrating Drink

When assessing different drinks, it's clear that the 'best' option depends on the situation. For daily hydration, plain water is still the most accessible, calorie-free choice. However, for rapid rehydration after significant fluid loss—such as from intense exercise, heat exposure, or illness—other options prove superior.

Oral Rehydration Solutions (ORS)

For medical-grade rehydration, especially when recovering from dehydration caused by vomiting or diarrhea, ORS are the most effective. These solutions contain a precise balance of water, glucose, and electrolytes (sodium, potassium, and chloride), which maximizes the body's ability to absorb fluid through a mechanism called sodium-glucose co-transport. The World Health Organization (WHO) has long advocated for ORS use, and studies confirm their high fluid retention rates.

Milk (Skim and Full-Fat)

Surprising to many, both skim and full-fat milk consistently rank higher on the BHI than water. The effectiveness is attributed to milk's natural composition of lactose (sugar), protein, and fat, which slows gastric emptying. Additionally, milk is a natural source of electrolytes like sodium and potassium, which help the body retain the fluid. Skim milk is particularly noted for its hydrating properties post-exercise, offering a blend of rehydration and protein for muscle repair.

Other Highly Hydrating Beverages

Coconut Water: A natural source of electrolytes like potassium and magnesium, coconut water is a great option for light rehydration. However, its electrolyte content is typically lower than in ORS.
Fruit Juices: Juices like orange or watermelon contain high water content and natural electrolytes. However, their high concentration of sugar can sometimes draw water into the intestines, potentially making them less hydrating than low-sugar alternatives and adding extra calories.
Sports Drinks: These are formulated for athletes engaged in intense or prolonged exercise (>60 minutes) to replenish carbohydrates and electrolytes lost through sweat. While effective for their specific purpose, they are often high in added sugar and are not as effective for general or illness-related dehydration as ORS.
Tea and Coffee: In moderation, caffeinated beverages like coffee and tea are not dehydrating and contribute to daily fluid intake. The diuretic effect only becomes significant with very high doses of caffeine.

Comparison of Key Hydration Drinks


Feature	Water	Oral Rehydration Solution (ORS)	Milk (Skim)	Sports Drink	Coconut Water
BHI Score	Reference (1.0)	High (~1.5)	High (~1.5)	Variable (~1.0)	Moderate
Electrolytes	None (unless added)	High & Balanced	Natural source (Na, K, Ca)	Replenishes (Na, K)	Natural source (K, Mg)
Carbohydrates	None	Specific Ratio (glucose)	Natural sugars (lactose)	High (glucose/sucrose)	Natural sugars
Protein/Fat	None	None	Contains Protein/Fat	None	Minimal
Best For	Daily Hydration	Illness (vomiting/diarrhea)	Post-Exercise Recovery	Intense, Prolonged Exercise	Light Rehydration
Cost	Low	Moderate	Moderate	Moderate to High	High

Practical Tips for Optimal Hydration

Listen to your body: The feeling of thirst is a reliable indicator that you need to drink. If you feel thirsty, you may already be mildly dehydrated.
Monitor urine color: A simple visual check can help. Your pee should be a pale, clear yellow. Darker urine indicates you need more fluids.
Hydrate for the occasion: Choose your drink based on your activity level and health needs. Water is fine for most everyday situations, but switch to ORS for illness or high-electrolyte options like milk or sports drinks after intense workouts.
Eat your water: About 20% of your daily fluid intake comes from foods. Water-rich fruits and vegetables like watermelon, strawberries, cucumber, and lettuce are excellent for hydration.
Time your intake: Drink throughout the day rather than chugging large amounts at once. It's especially important to rehydrate in the morning after waking up and before, during, and after exercise.
Flavor your water: If you dislike plain water, add fruit slices (lemon, lime, berries) or herbs (mint) to make it more appealing and help you drink more.

Conclusion

While plain water is the standard for everyday hydration, studies on the Beverage Hydration Index (BHI) show that drinks like skim milk and Oral Rehydration Solutions (ORS) can be even more hydrating in specific circumstances. Their ability to slow gastric emptying and deliver essential electrolytes helps the body retain fluid more effectively than water alone. For most people, water is sufficient for daily needs, but for rapid rehydration after intense exercise or illness, an ORS or a glass of milk may be a better choice. The key to optimal hydration lies in understanding the context and selecting the beverage that best suits your body's current needs.

For more detailed information on treating and preventing dehydration, resources such as those provided by the NHS offer comprehensive guidance on fluid intake for various situations, from daily life to recovery from illness. https://www.nhs.uk/conditions/dehydration/

Frequently Asked Questions

Yes, research using the Beverage Hydration Index (BHI) has shown that skim and full-fat milk are more hydrating than water. The protein, fat, and natural sugars in milk, along with its electrolytes like sodium and potassium, slow down the stomach's emptying, which leads to more prolonged fluid retention.

For mild to moderate dehydration, especially from illness like vomiting or diarrhea, an Oral Rehydration Solution (ORS) is the fastest way to rehydrate. Its specific balance of electrolytes and sugar maximizes fluid absorption in the intestines.

No. Sports drinks are designed for intense, prolonged exercise lasting more than 60 minutes, where both electrolytes and carbohydrates need replenishing. For most people and routine hydration, plain water is sufficient and avoids the added sugars and calories.

In moderate amounts, no. The fluid in coffee and tea contributes to your daily hydration. The diuretic effect of caffeine is mild and only becomes significant with very high consumption.

Yes, studies have found no difference in the hydrating effect of still versus sparkling water. The carbonation does not impact hydration levels, though some people may find the bubbles cause bloating, which could reduce overall intake.

Electrolytes are minerals that regulate fluid balance, nerve function, and muscle contractions. They help the body absorb and retain water, distributing it properly inside and outside the cells. Losing electrolytes through sweat or illness can impair hydration.

No. While they contain water, their high sugar concentration can be counterproductive for hydration. The high sugar can pull water into the small intestine during digestion, potentially worsening fluid balance, especially in cases of diarrhea.