Can You Drink Water on a 17 Hour Fast?: Understanding Hydration During Intermittent Fasting

October 13, 2025 •

4 min read

According to the National Institutes of Health, drinking water during an intermittent fast is generally permitted because it does not affect blood sugar or insulin levels. In fact, staying hydrated is crucial for maintaining energy levels and preventing common side effects during your fasting window, directly answering the question: can you drink water on a 17 hour fast?

Quick Summary

Yes, water is essential during a 17-hour fast, helping maintain hydration and curb hunger without breaking the fasted state. This is especially important as your body sheds water during fasting. Other calorie-free beverages like black coffee and unsweetened tea are also permitted.

Key Points

Yes, you can drink water: Drinking water is essential during a 17-hour fast and will not break your fasted state.
Replenish fluid loss: During fasting, your body excretes water bound to glycogen stores, making consistent hydration crucial.
Stick to zero-calorie fluids: Water, black coffee, and unsweetened tea are safe to consume during your fasting window.
Avoid sugary and caloric drinks: Sodas, juices, and coffee with additives will break your fast and should be avoided.
Add electrolytes for longer fasts: For extended fasts or intense exercise, a pinch of sea salt can help replenish lost minerals.
Listen to your body: Pay attention to signs of dehydration like dark urine, headaches, or dizziness, and adjust your water intake accordingly.

The Essentials of Hydration During a 17-Hour Fast

Intermittent fasting, particularly time-restricted eating models like the 17/7 protocol, has gained significant popularity. This eating pattern involves a 17-hour fasting window followed by a 7-hour eating window. A key component for success and safety in this regimen is proper hydration. While the goal is to abstain from calories, water is a non-caloric liquid that plays a vital role in bodily functions, even during a fast. Understanding why and how to hydrate correctly is fundamental to a positive fasting experience.

The Science Behind Fasting and Water Loss

During a fast, your body undergoes several metabolic shifts that affect your fluid balance. When you stop eating, your insulin levels drop. This prompts your kidneys to excrete more sodium and water, a process known as natriuresis. Furthermore, your body uses its stored energy reserves, starting with glycogen. Each gram of stored glycogen is bound to 3-4 grams of water. As glycogen stores are depleted, this water is released and flushed from the body, leading to increased urination and potential dehydration if not replenished. This makes active water intake even more critical during fasting periods to prevent dehydration and its associated symptoms.

What to Drink and What to Avoid During a Fast

To maintain the fasted state and maximize benefits, you must stick to zero-calorie beverages. Fortunately, your options aren't limited to plain water.

Permitted Beverages

Plain Water: Still or sparkling, water is the number one choice for hydration. It has no calories and provides essential fluids.
Black Coffee: Unsweetened black coffee is generally allowed. It contains antioxidants and can act as an appetite suppressant for some. However, the effect of artificial sweeteners is debated, so it's safest to avoid them.
Unsweetened Tea: Green, black, and herbal teas (without sweeteners or milk) are excellent options. They offer flavor variety and hydration.
Plain Sparkling Water: As long as it has no added sweeteners or calories, plain sparkling water is a refreshing, fast-friendly option.

Beverages That Will Break a Fast

Any drink containing calories, sugar, or other additives should be avoided as it will prompt an insulin response, breaking the fasted state. Examples include:

Soda and sports drinks
Juice and smoothies
Coffee or tea with milk, cream, or sugar
Alcohol
Coconut water (contains sugar and carbs)

Practical Tips for Staying Hydrated During a 17-Hour Fast

Drink consistently: Don't wait until you feel thirsty. Keep a water bottle with you and sip throughout the day to ensure a steady intake.
Monitor your urine: A pale yellow color indicates good hydration. Darker urine suggests you need more fluid.
Consider electrolytes: For longer fasts or if you exercise, your body may excrete more electrolytes. A pinch of high-quality salt in your water can help replenish these minerals.
Experiment with temperature: Some find that warm water or herbal tea is more soothing to an empty stomach than cold beverages.
Listen to your body: If you feel dizzy, lightheaded, or experience persistent headaches, it could be a sign of dehydration.

Comparison of Fast-Friendly and Non-Fast-Friendly Drinks


Drink Type	Fast-Friendly?	Calories	Notes
Plain Water	Yes	0	The best option for hydration.
Black Coffee	Yes	0	Can help with energy and hunger, but avoid additives.
Herbal Tea	Yes	0	Unsweetened varieties are great for flavor and hydration.
Plain Sparkling Water	Yes	0	A refreshing, calorie-free alternative to still water.
Seltzer with Artificial Sweeteners	Generally No	0	Some purists believe artificial sweeteners can trigger an insulin response. Avoid them for a cleaner fast.
Lemon Water	Debateable	Low	Contains a small number of calories. Some say a small squeeze is fine, others avoid it completely.
Bone Broth	No (Usually)	Low	While nutrient-dense, it has calories and technically breaks a fast. Best for longer fasts to replenish nutrients.
Soda or Juice	No	High	Will immediately break your fast due to sugar content.

Potential Risks and How to Mitigate Them

While drinking water is safe and necessary, intermittent fasting isn't suitable for everyone. Pregnant or breastfeeding women, individuals with a history of eating disorders, children, and those with certain medical conditions like diabetes should consult a healthcare professional before starting. Even for healthy adults, insufficient hydration can lead to side effects like headaches, fatigue, and irritability. The key is to be proactive with fluid intake and listen to your body.

Conclusion: Stay Hydrated, Stay Healthy

For a 17 hour fast, drinking water is not only allowed but actively encouraged for a successful and safe experience. Water provides crucial hydration, helps manage hunger signals, and supports bodily functions without breaking your fast. By understanding which beverages are permissible and following smart hydration practices, you can minimize side effects and optimize your fasting routine. Always consult a healthcare provider before beginning any new dietary regimen to ensure it aligns with your health needs. Focusing on plain water and other calorie-free liquids during your fasting window is the simplest and most effective strategy for staying properly hydrated.

Visit the Cleveland Clinic for more tips on fasting safely.

Frequently Asked Questions

No, drinking plain water does not break a fast. Since it contains zero calories, it does not trigger an insulin response and allows your body to remain in a fasted state.

Not drinking enough water during a fast can lead to dehydration, which may cause headaches, fatigue, dizziness, and low energy levels. These symptoms can make fasting more difficult.

This is a point of debate. A squeeze of lemon adds a few calories. While some find this acceptable, strict fasters avoid it. For a pure fast, stick to plain water.

Yes, other permitted, zero-calorie beverages include black coffee and unsweetened herbal or black tea. Avoid any milk, sugar, or artificial sweeteners.

A general guideline is to listen to your body and aim for enough water so that your urine is pale yellow. A recommended starting point is around 8-12 cups per day, adjusted for individual factors like activity level and climate.

No, a small pinch of high-quality salt, like sea salt, will not break your fast. It is often recommended to help replenish electrolytes lost during fasting, especially during longer fasts.

It is best to avoid diet sodas and artificial sweeteners during a fast. While they are calorie-free, some research indicates they can trigger an insulin response or increase hunger cravings, potentially interfering with the fasting process.