What is the best liquid to rehydrate and replenish your body?

December 11, 2025 •

4 min read

The human body is composed of approximately 50-70% water, and losing just a small percentage of this fluid can lead to dehydration, impacting everything from energy levels to cognitive function. While many people reach for a bottle of plain water, the optimal liquid for rehydration depends on the cause and severity of your fluid loss.

Quick Summary

The ideal rehydration liquid varies based on your level of dehydration and electrolyte loss. Water is great for mild cases, while oral rehydration solutions or milk are superior for replenishing lost fluids and key minerals more effectively and for longer periods.

Key Points

ORS is Optimal for Moderate Dehydration: Oral Rehydration Solutions (ORS) with balanced salts and glucose are the most effective for recovering from significant fluid and electrolyte loss due to illness like diarrhea or vomiting.
Water is Best for Mild Cases: Plain water is perfectly suitable for preventing dehydration and rehydrating after light exercise or daily activities, but it may not be enough for moderate or severe fluid loss.
Milk Offers Prolonged Hydration: Studies show milk is more hydrating than water over longer periods due to its natural sugar, protein, and fat content, which slows gastric emptying.
Severe Dehydration Needs Medical Care: For severe dehydration symptoms such as confusion or rapid heart rate, seek immediate medical attention as intravenous fluid replacement may be necessary.
Electrolytes are Key: When rehydrating, replacing lost electrolytes like sodium and potassium is as important as replacing lost water, especially after heavy sweating or illness.
High-Sugar Drinks Can Be Detrimental: Excessively sugary drinks, including undiluted sports drinks for non-athletes, can sometimes worsen dehydration due to their osmotic effect.

Understanding the Science of Rehydration

Rehydration isn't just about replacing lost water; it's about restoring the balance of electrolytes—minerals like sodium, potassium, and chloride—that are crucial for nerve function, muscle contraction, and maintaining fluid balance. When we sweat, vomit, or have diarrhea, we lose both water and electrolytes. Drinking only plain water to rehydrate can sometimes dilute the remaining electrolytes in the body, potentially leading to a dangerous condition called hyponatremia. This is where the composition of a rehydration drink becomes critical.

The gut uses a specific mechanism to absorb water efficiently. Water absorption is facilitated by the co-transport of glucose and sodium in the small intestine, a process that moves hundreds of water molecules for every sodium and glucose ion absorbed. This is why oral rehydration solutions (ORS) and other drinks containing a balanced mix of salts and sugars are so effective, especially during moderate to severe fluid loss. The added glucose (sugar) helps accelerate the absorption of sodium and water, making these drinks far superior to plain water for rapid rehydration.

The Best Liquids for Different Scenarios

Your choice of rehydration liquid should match your situation. A professional athlete after an intense workout will have different needs than someone recovering from a stomach flu.

For Mild Dehydration (Everyday or Light Exercise)

For routine hydration and mild fluid loss, plain water remains an excellent and sufficient choice. It contains no calories or added sugars and is easily accessible.

Plain Water: The simplest and most accessible option. It works well for preventing dehydration and for fluid replacement after low-intensity or short-duration activity.
Fruit-Infused Water: Adding lemon, lime, or cucumber to water can make it more palatable, encouraging you to drink more. It adds minimal nutrients but can significantly increase water intake.
Water-Rich Foods: Eating foods with high water content, such as watermelon, oranges, or cucumbers, contributes significantly to your daily fluid intake.

For Moderate Dehydration (Illness or Intense Exercise)

When fluid loss is more substantial, such as from vomiting, diarrhea, or intense exercise lasting longer than an hour, simply drinking plain water is not enough. You need to replace lost electrolytes.

Oral Rehydration Solutions (ORS): These are scientifically formulated to have the optimal balance of sodium, potassium, and glucose for rapid absorption. Brands like Pedialyte or commercial powders are highly effective and are the gold standard for treating illness-related dehydration, especially in children and the elderly.
Sports Drinks: Products like Gatorade or Powerade can be beneficial for athletes engaged in prolonged, high-intensity exercise. The carbohydrates provide energy, while electrolytes replace those lost in sweat. However, they can be high in sugar, so they are not ideal for general hydration needs.
Coconut Water: A natural source of electrolytes, particularly potassium. It is lower in sugar than most sports drinks and provides a good electrolyte balance for moderate dehydration, though it is not as high in sodium as an ORS.
Milk: Surprisingly, a study from Scotland's St. Andrews University found that milk is more hydrating than plain water due to its lactose, protein, and fat content, which slows fluid emptying from the stomach. Skim milk, in particular, was found to be highly effective for post-exercise rehydration.

For Severe Dehydration

Severe dehydration is a medical emergency and requires immediate hospital treatment. This often involves intravenous (IV) fluids to rapidly restore blood volume and electrolyte balance under medical supervision. Symptoms of severe dehydration can include dizziness, rapid heart rate, confusion, or fainting.

Comparison of Rehydration Liquids


Liquid	Best For	Key Ingredients	Hydration Efficacy	Notes
Plain Water	Mild dehydration, daily intake	H₂O	Good (Short-term)	Best for prevention and mild fluid loss.
Oral Rehydration Solution (ORS)	Moderate dehydration (illness), post-exercise	Water, electrolytes, glucose	Excellent (Rapid Absorption)	Optimal for illness (diarrhea/vomiting) and moderate fluid loss.
Sports Drink	Intense, prolonged exercise	Water, electrolytes, carbohydrates	Excellent (with caveats)	High in sugar; best used only during and after strenuous activity.
Milk (Skim)	Post-exercise recovery	Water, electrolytes, protein, fat	Excellent (Longer-lasting)	Protein and fat aid in prolonged fluid retention.
Coconut Water	Moderate fluid loss (natural option)	Water, potassium, trace electrolytes	Good	Natural, lower sugar option. Lacks higher sodium needed for intense loss.
Broth-Based Soups	Illness, general rehydration	Water, sodium, other minerals	Good	Provides sodium and warmth, especially soothing during illness.

Creating Your Own DIY Electrolyte Drink

For a natural, low-cost alternative, you can create your own oral rehydration solution at home. Be sure to use clean, safe water and measure ingredients accurately to maintain the proper balance of electrolytes. Always consult a medical professional before relying on homemade solutions, especially for children or in cases of significant fluid loss.

Simple Homemade Rehydration Drink

1 liter clean water
1/2 teaspoon salt
6 teaspoons sugar
Optional flavoring with a splash of fruit juice Mix until salt and sugar are fully dissolved. Sip slowly to avoid stomach upset.

Conclusion

While plain water is the foundation of daily hydration, it is not always the best liquid to rehydrate, particularly when significant electrolytes have been lost due to illness or intense physical activity. For quick and effective rehydration, especially when recovering from vomiting or diarrhea, commercially prepared Oral Rehydration Solutions (ORS) are the most effective choice due to their scientifically-proven formulation of salts and sugars. For athletes, sports drinks offer carbohydrates and electrolytes, and interestingly, skim milk is a highly effective, longer-lasting hydrator. Choosing the right fluid for the right situation is key to restoring your body's balance and recovering effectively.

For more detailed guidance on severe dehydration and clinical management, the National Library of Medicine provides excellent resources on the principles of rehydration therapy for medical professionals and patients. [https://www.ncbi.nlm.nih.gov/books/NBK63837/]

Frequently Asked Questions

Plain water is not the best choice when you have lost significant electrolytes through heavy sweating, vomiting, or diarrhea. In these situations, drinks with added electrolytes and a small amount of sugar, like an Oral Rehydration Solution (ORS), are more effective for restoring balance.

For athletes engaged in prolonged, intense exercise (more than an hour), sports drinks can be better because they replace electrolytes and provide carbohydrates for energy. For general rehydration or mild dehydration, plain water is the healthier, lower-sugar option.

Yes, you can make a simple rehydration drink at home by mixing a liter of clean water with half a teaspoon of salt and six teaspoons of sugar. However, for children or serious fluid loss, commercial ORS products are more precisely balanced and therefore safer.

Milk is effective for rehydration because it contains water, electrolytes (like sodium and potassium), and macronutrients (protein, fat, and lactose). This combination helps the body retain fluid for a longer period compared to plain water.

An ORS is recommended for treating mild to moderate dehydration caused by gastroenteritis (vomiting and/or diarrhea) in adults and children. It has a specific ratio of salts and glucose to maximize fluid absorption in the gut.

Avoid drinks with high levels of caffeine, alcohol, or excessive sugar, as these can have a diuretic effect and potentially worsen dehydration. Examples include coffee, energy drinks, alcoholic beverages, and some very sugary sodas.

The time it takes to rehydrate depends on the severity of dehydration. For mild cases, you might feel better within an hour or two. For more significant fluid loss, it can take several hours of consistent fluid intake. Severe dehydration requires immediate medical attention.