Can You Drink Water During the 16 Hours of Intermittent Fasting?

October 31, 2025 •

3 min read

According to health experts at Johns Hopkins, zero-calorie beverages like water are permitted during fasting periods. This is great news for anyone on the popular 16/8 schedule, confirming that you can drink water during the 16 hours of intermittent fasting to stay properly hydrated. In fact, staying hydrated is crucial for preventing negative side effects and maximizing the benefits of your fast.

Quick Summary

This article explains why water is not only allowed but necessary during intermittent fasting periods to maintain hydration and support bodily functions. It clarifies what constitutes breaking a fast and provides guidelines for proper hydration, including recognizing signs of dehydration, consuming electrolytes, and understanding how water helps control hunger.

Key Points

Water is Allowed: Plain water is a zero-calorie beverage and can be consumed freely during the 16 hours of intermittent fasting.
Hydration is Crucial: During fasting, your body loses water due to metabolic changes, making consistent hydration even more important to prevent dehydration.
Watch for Dehydration: Symptoms like headaches, dizziness, and dark urine are signs you need more water, and staying hydrated can help curb hunger.
Monitor Urine Color: A good indicator of proper hydration is pale yellow to clear urine.
Other Fast-Friendly Drinks: Options like black coffee, unsweetened tea, and sparkling water are also generally acceptable during the fasting window.
Avoid Sugars and Calories: Any drink with calories, including milk, juice, and sugary sodas, will break your fast and should be avoided.
Electrolyte Balance: Consider adding a pinch of high-quality salt to your water during prolonged fasts or strenuous activity to replenish lost electrolytes.
Listen to Your Body: Individual hydration needs vary, so pay attention to your body’s signals to avoid both dehydration and overhydration.

The Non-Caloric Rule of Fasting

When engaging in intermittent fasting, the fundamental principle is to avoid consuming calories during your fasting window. Since plain water contains zero calories, it will not trigger an insulin response or break your fast. For many, the 16/8 method is a popular choice, and during the 16-hour fasting period, water is your best friend. It is crucial for maintaining bodily functions and supporting your overall health.

Why Hydration is More Important During Fasting

During a fast, your body undergoes a process called metabolic switching, where it transitions from burning glucose to burning stored fat for energy. This metabolic shift affects your hydration in a couple of ways.

Glycogen Breakdown: Your body stores carbohydrates in the form of glycogen, which is bound to water molecules. As your body breaks down these glycogen stores for energy, it releases the associated water, which is then eliminated, increasing your risk of dehydration.
Increased Sodium Excretion: Dropping insulin levels during a fast can cause your kidneys to excrete more sodium, which in turn leads to increased water loss through urination. This natural diuretic effect, while beneficial for reducing water retention, makes consistent fluid intake even more necessary.

Recognizing and Preventing Dehydration

Proper hydration is key to a comfortable and successful fast. Recognizing the signs of dehydration early can help you avoid potential issues.

Common signs of dehydration:

Dark yellow or amber-colored urine
Dry mouth and lips
Headaches and dizziness
Fatigue and low energy
Constipation
Increased thirst

If you experience any of these symptoms, it's a clear signal that you need to increase your fluid intake. For those who are more active, live in a hot climate, or are just starting out, keeping a close watch on these signs is especially important.

How Much Water Should You Drink?

While the standard advice is often around 8 glasses a day, your needs during intermittent fasting might be different. Some experts suggest drinking an additional cup of water for every hour you are fasting, especially on a 16/8 schedule. However, it is important to find a balance and listen to your body. Personal factors such as activity level, climate, and overall health will influence your specific hydration needs. A good rule of thumb is to monitor your urine color; it should remain pale yellow to clear throughout the day.

Comparison: Water vs. Other Fasting-Friendly Drinks


Beverage Type	Calories	Does It Break a Fast?	Added Benefits	Potential Drawbacks
Plain Water	0	No	Essential hydration, supports metabolism, curbs hunger	No added nutrients or flavor
Black Coffee	<5 per cup	No	Appetite suppression, enhanced fat burning, improves brain function	Can trigger acidity and dehydration if consumed in excess
Unsweetened Tea	<5 per cup	No	Antioxidant benefits, soothing	Some herbal teas may have minimal calories; check labels
Sparkling Water	0	No	Variety, refreshing alternative to plain water	Some flavored versions may contain sweeteners; read labels carefully

Other Fasting-Friendly Options

Besides plain water, unsweetened tea, and black coffee, there are a few other options that typically won't break your fast. These include sparkling water (without added sweeteners), herbal teas, and a squeeze of lemon or lime in your water for flavor. However, beverages with significant calories, such as fruit juice, milk, and sugary sodas, should be avoided during the fasting window as they will break the fast. Some people also add a pinch of salt to their water to replenish lost electrolytes.

Conclusion

To put it simply, drinking water during the 16 hours of intermittent fasting is not only allowed but strongly recommended. The zero-calorie nature of plain water ensures it won't interfere with the metabolic state of your fast, while proper hydration is critical for your overall well-being and for managing potential side effects like headaches or fatigue. By incorporating plenty of water and other zero-calorie liquids like black coffee and unsweetened tea, you can make your fasting experience more comfortable and effective. Always listen to your body and adjust your fluid intake based on your activity level and the climate. For those with underlying health conditions, it is always best to consult with a healthcare professional before starting any fasting regimen.

Frequently Asked Questions

Yes, drinking water can be an effective strategy to manage hunger. Sometimes the body mistakes thirst for hunger, and having a glass of water can help you feel more satiated and comfortable during your fasting window.

A common guideline is to drink at least 8 to 10 glasses of water per day, but you may need more while fasting due to increased fluid loss. Pay attention to your body's signals and the color of your urine to gauge your personal needs.

A small squeeze of lemon or lime is generally fine, as the calorie content is negligible and will not break your fast. It can be a refreshing way to add flavor and make plain water more enjoyable.

Sparkling water is acceptable as long as it contains no added sweeteners or calories. You should always check the nutrition label for any flavored water to ensure it is calorie-free, as hidden sugars can break your fast.

Yes, black coffee and unsweetened tea are widely considered safe for intermittent fasting. Both contain minimal calories and can help with appetite suppression and increased energy.

Dry fasting, which prohibits all liquids including water, is often practiced for religious reasons but carries significant health risks like dehydration. Most health experts advise against it without medical supervision, and for most goals, a traditional fast with water is both safer and more effective.

While less common than dehydration, overhydration can occur, leading to a dangerous condition called hyponatremia (diluted sodium levels). Symptoms include nausea, headaches, and confusion. Listen to your body and moderate your intake, especially if you add electrolytes.