How many calories are in an 8 ounce glass of water? (Answered)

January 14, 2026 •

3 min read

According to the Centers for Disease Control and Prevention (CDC), plain water has zero calories and is recommended to replace sugary beverages to reduce caloric intake. So, how many calories are in an 8 ounce glass of water? The answer is none, assuming it's pure, unflavored water.

Quick Summary

This guide explains the scientific reason behind water's zero-calorie content and explores the differences between various water types, including plain, mineral, and flavored versions. It also discusses the health benefits of choosing water and provides insights into common myths about water and caloric intake.

Key Points

Zero Calorie Content: A glass of plain, unflavored water contains zero calories, as it provides no macronutrients like carbs, proteins, or fats.
Macronutrient Basis: Calories are a measure of energy derived from macronutrients. Water, being H₂O, lacks the energy-rich chemical bonds to provide fuel.
Types of Water: While plain, mineral, and unsweetened sparkling waters are calorie-free, flavored waters and tonic water can contain significant added sugar and calories.
Weight Management Tool: Replacing sugary drinks with zero-calorie water is a simple and effective strategy for reducing overall caloric intake and managing weight.
Not a Metabolism Booster: The idea that drinking ice water burns significant calories is a myth; the thermogenic effect is minimal and not an effective weight loss method.
Always Read the Label: When choosing bottled or flavored water products, check the nutrition label to ensure there are no hidden sugars or caloric additives.

The Science Behind Water’s Zero Calories

The fundamental reason that water contains no calories is its chemical composition. A calorie is a unit of energy that the body can use for fuel, and these calories come from the macronutrients in our diet: carbohydrates, proteins, and fats. The molecular formula for water is H₂O—two hydrogen atoms and one oxygen atom. Crucially, water lacks the carbon-based chemical bonds that store usable energy, which are found in macronutrients. Since our bodies cannot metabolize or break down water to produce energy, it has a caloric value of zero.

The Role of Macronutrients

To understand why water is calorie-free, it is helpful to look at where calories do come from. Macronutrients are the main components of food that provide energy:

Carbohydrates: Provide about 4 calories per gram and are the body's primary energy source.
Proteins: Also provide about 4 calories per gram and are essential for building and repairing tissues.
Fats: Offer a more energy-dense source, with about 9 calories per gram.

Since plain water is composed solely of hydrogen and oxygen, with no carbohydrates, fats, or proteins, it contributes nothing to your daily energy intake. This principle holds true regardless of the water's temperature, physical state (liquid, ice, or steam), or origin (tap, bottled, or filtered).

Comparison of Water Types and Their Caloric Content

It is important to distinguish between pure water and other water-based beverages, as many popular drinks contain added calories from sweeteners or other ingredients. The table below outlines the caloric differences between common water types.


Water Type	Calories per 8 oz (237 ml)	Notes
Plain/Still Water	0	The standard zero-calorie option.
Sparkling/Carbonated Water	0	Calorie-free unless sugars or flavors are added.
Mineral Water	0	Contains natural minerals but no calories.
Tonic Water	90–124	Contains added sugar and sweeteners.
Flavored/Vitamin Water	Varies (0–120)	Calorie count depends on added sugar and ingredients. Always check the label.
Coconut Water	~46	Contains natural sugars from the coconut.
Fruit-Infused Water (DIY)	<5	Negligible calories unless the fruit is consumed.

Health Benefits of Choosing Zero-Calorie Water

Opting for water over high-calorie beverages has significant health benefits, especially for weight management.

Staying hydrated: Water is crucial for countless bodily functions, including regulating body temperature, lubricating joints, and transporting nutrients.

Weight management: Replacing caloric drinks like soda or juice with water can drastically reduce your overall calorie consumption. Some studies suggest drinking water before meals can also promote a feeling of fullness, potentially leading to lower food intake.

Cognitive function: Even mild dehydration can impair cognitive function, affecting mood, memory, and concentration. Drinking water throughout the day keeps your brain performing optimally.

Flushing out waste: Your body uses water to excrete waste through sweat and urination, which is essential for proper kidney function and flushing out toxins.

The Myth of Thermogenesis

A common myth suggests that drinking ice-cold water can burn a significant number of calories because your body must expend energy to warm it up. While technically true, the effect is minimal and not a viable strategy for weight loss. The energy used to heat one glass of ice water is only around 4–7 calories, which is an insignificant amount in the context of a person's daily caloric expenditure. This does not impact your weight in any meaningful way.

Making Water Your Go-To Beverage

For those who find plain water unappealing, there are several zero-calorie options to increase your water intake without adding sugar.

Infuse with fruit: Add slices of cucumber, lemon, lime, or berries for a refreshing, calorie-free flavor.
Herbal tea: Unsweetened herbal teas, served hot or cold, offer a variety of flavors with no calories.
Sparkling water: Unflavored sparkling or carbonated water provides a bubbly alternative to still water without any added calories.

Conclusion

In conclusion, an 8 ounce glass of pure water contains zero calories because it is devoid of the macronutrients—carbohydrates, fats, and proteins—that provide the body with energy. This makes it the ideal, calorie-free choice for staying hydrated and supporting overall health and weight management goals. Always check the nutrition labels of flavored or enhanced water products, as added sugars can quickly introduce a significant number of calories. By choosing pure water, you benefit from essential hydration without any caloric cost.

Frequently Asked Questions

No, plain sparkling water is calorie-free. Calories are only present if sugars, flavorings, or other caloric ingredients have been added to the beverage.

No, the calorie content of water is zero regardless of its temperature. Your body uses a very small amount of energy to heat cold water, but this effect is not significant for calorie intake or weight loss.

Water is recommended for weight loss because it has zero calories and can help promote a feeling of fullness. By replacing high-calorie beverages with water, you can reduce your daily caloric intake.

No, minerals naturally present in water, such as calcium and magnesium, do not contain calories. Therefore, mineral water is still a zero-calorie beverage.

While it is rare, excessive water intake can lead to a condition called water intoxication, which can dilute critical electrolytes in the blood. However, this is unlikely under normal circumstances.

You can add flavor to water without calories by infusing it with slices of fruit (like lemon or cucumber), herbs (like mint), or by using natural, unsweetened herbal tea.

Unlike regular water, coconut water contains natural sugars and therefore has calories, typically around 46 calories per 8-ounce cup. Always read the label to be sure.