What will hydrate you faster than water? The science of electrolyte-rich fluids

October 5, 2025 •

4 min read

According to a 2015 study, milk has been shown to be more hydrating than plain water over a longer period, primarily because of its unique nutritional composition. This surprising finding addresses the common question of what will hydrate you faster than water and highlights the fact that fluid intake involves more than just H2O.

Quick Summary

Oral rehydration solutions (ORS) and milk are often more effective for rehydration than plain water because they contain electrolytes, sugars, and protein that aid in fluid absorption and retention. For rapid recovery from intense exercise, heat exposure, or illness, strategically choosing a beverage with the right composition is key.

Key Points

ORS is Faster for Illness: Oral rehydration solutions (ORS), with their optimal mix of glucose and sodium, are absorbed by the body faster than plain water, making them ideal for treating moderate dehydration from vomiting or diarrhea.
Milk Provides Sustained Hydration: Due to its protein, fat, and lactose content, milk slows gastric emptying, leading to a more gradual and prolonged rehydration effect compared to water.
Electrolytes are Crucial: When rehydrating after significant sweat loss, replacing electrolytes like sodium and potassium is as important as replacing water, as plain water alone can dilute blood sodium levels.
Timing and Volume Matter: Drinking a larger volume of fluid at one time can speed up gastric emptying and absorption, but sipping fluids regularly is a better strategy for consistent, preventative hydration.
Foods Contribute to Hydration: About 20% of your daily fluid intake comes from food, with fruits and vegetables like watermelon, cucumber, and lettuce being excellent, water-rich sources.
Water is Best for Mild Cases: For most everyday situations and mild dehydration, plain water remains the most accessible, inexpensive, and healthiest option.
Context is Key: The most effective rehydration strategy depends on the cause of fluid loss, whether it's due to illness, intense exercise, or normal daily activities.

Understanding the Mechanics of Rapid Hydration

While water is the body's primary fluid source, its rehydration speed depends on several factors, including absorption rate and fluid retention. The key to hydrating faster than plain water lies in a drink's contents. Specifically, a precise combination of electrolytes (minerals like sodium and potassium) and carbohydrates can significantly improve how quickly and efficiently the body absorbs and retains fluid. When fluids enter the body, they must pass through the stomach and into the small intestine for absorption. A beverage with a balanced concentration of solutes can optimize this process, known as gastric emptying, and enhance the transport of water into the bloodstream.

The Role of Electrolytes and Glucose

For moderate dehydration—such as from illness or extensive sweating—the body doesn't just lose water; it loses vital electrolytes like sodium and potassium. Oral Rehydration Solutions (ORS) are scientifically formulated to restore this balance. An ORS works on the principle of sodium-glucose cotransport, where the glucose helps the small intestine absorb both sodium and water more efficiently. This is why ORS is often more effective than plain water at replenishing fluids quickly and is recommended by health organizations like the WHO.

Milk: A Sustained Hydration Champion

A study from St. Andrews University found that both skim and whole milk were more hydrating than water over a period of 3-4 hours. The reason lies in milk's unique nutrient profile:

Natural Sugar (Lactose): Acts similarly to the glucose in ORS, aiding in water and sodium absorption.
Protein and Fat: Help slow the emptying of fluid from the stomach, which allows for more gradual and sustained hydration over time, rather than a rapid flush that leads to quicker urination.
Sodium: Helps the body hold onto the fluid, reducing urine output and promoting longer-lasting rehydration.

Other Hydrating Beverages and Considerations

Beyond ORS and milk, several other fluids can contribute to faster or more sustained hydration, depending on the situation. For instance, coconut water is rich in potassium and can be a good source of electrolytes, though it is lower in sodium than traditional sports drinks. Fruit and vegetable juices also contain water and electrolytes but can be high in sugar and calories. Smoothies, especially those with fruits and dairy, combine fluid with nutrients and fiber, which helps slow absorption. For most people, water is sufficient for everyday hydration, but specialized drinks offer a distinct advantage during and after strenuous activities or illness.

Comparison of Hydrating Beverages


Beverage	Primary Hydration Mechanism	Key Advantages	Best For	Potential Drawbacks
Oral Rehydration Solution (ORS)	Optimized balance of glucose and sodium for rapid absorption.	Fastest absorption rate, replaces critical electrolytes lost from illness.	Moderate dehydration from vomiting or diarrhea.	Unnecessary for mild dehydration; can cause salt toxicity if used improperly.
Milk (Skim or Whole)	Natural electrolytes, proteins, fats, and lactose slow gastric emptying.	Sustained, long-term hydration; provides added protein and calcium.	Post-exercise recovery; general hydration.	Heavier on the stomach; unsuitable for those with lactose intolerance.
Sports Drinks	Water with carbohydrates and electrolytes to fuel and rehydrate.	Convenient for long, intense workouts to replenish glycogen and fluids.	High-intensity exercise lasting over 60 minutes.	Often high in added sugars and calories.
Coconut Water	Natural electrolytes, especially potassium, with moderate sugar.	Lower in sugar than many sports drinks; naturally sourced minerals.	Mild rehydration; moderate exercise.	Low sodium content means it may not be ideal for replacing heavy sweat loss.
Plain Water	Replenishes lost fluid volume.	Inexpensive, calorie-free, and always accessible.	Everyday hydration for most people under normal conditions.	Ineffective for replacing lost electrolytes; can dilute blood sodium if consumed in excess during intense exercise.

Optimizing Your Hydration Strategy

Choosing the right beverage for hydration depends heavily on the context. While ORS provides the fastest rehydration for significant fluid and electrolyte loss due to illness, milk offers more sustained benefits for slower, longer-lasting fluid replacement. For athletes, sports drinks target both fluid and glycogen replenishment. For general health, a balanced diet including water-rich fruits and vegetables like watermelon and cucumbers can contribute significantly to overall hydration. The timing of consumption is also important; sipping fluids throughout the day is often more effective than chugging a large amount at once.

Conclusion

While plain water is essential for daily fluid intake, it is not always the fastest way to rehydrate. Beverages containing a precise blend of electrolytes and carbohydrates, such as Oral Rehydration Solutions, can accelerate fluid absorption by optimizing processes in the digestive tract. Other options like milk offer slower, more prolonged rehydration due to their nutrient composition. Ultimately, the most effective hydration strategy is personalized and should be adapted to your specific needs, considering factors like physical activity level, climate, and overall health. For moderate to severe dehydration, especially in cases of illness, turning to an ORS is a scientifically-backed approach to rapid recovery. For exercise or daily life, incorporating a variety of hydrating foods and drinks ensures a balanced approach. To learn more about oral rehydration therapy, visit the World Health Organization website.

Frequently Asked Questions

An Oral Rehydration Solution (ORS) is a scientifically formulated drink containing a precise ratio of water, glucose, and electrolytes like sodium and potassium. This composition is designed to maximize fluid absorption in the intestines, making it highly effective for treating dehydration caused by illness.

Milk is more hydrating over a longer period because its content of protein, fat, and lactose slows down how quickly the fluid leaves the stomach. This allows for a more sustained release into the bloodstream, and its sodium content helps the body retain the fluid.

In certain situations, yes. For endurance athletes or those in hot climates with significant sweat loss, sports drinks with carbohydrates and electrolytes can be more effective than water at restoring fluid balance and energy stores. However, their high sugar content makes them unnecessary for most casual exercise or mild dehydration.

Coconut water is a good source of natural electrolytes, particularly potassium. It is often lower in sugar than many commercial sports drinks. However, because it is low in sodium, it may not be the most effective choice for replacing electrolytes lost during very intense or prolonged exercise with heavy sweating.

Yes, but store-bought ORS is typically the safer and more balanced option, especially for treating illness-related dehydration. However, you can create a simple electrolyte drink with water, a small amount of salt, and fruit juice. It is not recommended to use homemade solutions for severe dehydration.

You should consider an ORS if you are experiencing moderate dehydration, typically caused by persistent vomiting or diarrhea, as it will replace lost electrolytes more effectively than water alone. For severe dehydration, medical intervention may be necessary.

Yes, excessive water intake can lead to a dangerously low blood sodium level, a condition called hyponatremia. This is most common in endurance athletes who drink large amounts of plain water during prolonged events. It can cause swelling of brain cells and, in severe cases, can be fatal.