Can You Drink Water While Fasting?

author avatar Dr. Eric Berg 08/31/2023

Fasting has many health benefits and has helped countless people to achieve healthy body weight, lower blood pressure, and enhance brain functions. 

It’s clear that fasting involves abstinence from solid food, but can you drink water while fasting? 

Learn why drinking water is essential while fasting and how adding electrolytes and sea salt to your water helps to get the most out of your fasting practice.  

Glass of water on a plate

Can you drink water while fasting?

Yes, you can drink water during a fast. Plain water doesn’t contain calories and won’t impact blood sugar levels, making it safe to drink while fasting.

In fact, drinking water during your fasting periods is essential to maintain healthy fluid levels, support normal kidney function, and helps to flush out toxins. 

However, plain water isn’t all your body needs during fasting. When you restrict caloric intake to promote fat burning, a process called metabolic switching, your liver triggers glycogen shedding, which can cause fluid loss and electrolyte imbalances

Glycogen shedding refers to the depletion of glycogen, a form of glucose bound to water that’s stored in muscles and the liver. During fasting periods, glycogen is metabolized, which releases large quantities of water. 

When your kidneys eliminate excess fluids, they also excrete essential electrolytes such as sodium, potassium, magnesium, and calcium.

Electrolytes are crucial for maintaining fluid balance, promoting normal muscle and cellular functions, and supporting energy production. 

Dehydration and electrolyte imbalances are among the most common causes of fasting-related fatigue, headaches, and muscle cramps.   

Here are three different types of fasting and what steps you can take to stay hydrated.

Intermittent fasting

Many people practice intermittent fasting, a popular mealtime schedule that alternates between fasting periods and time-restricted eating windows. 

A 16:8 fast (16 hours of fasting followed by eight hours of eating) is one of the most common intermittent fasting schedules and a widespread weight loss practice. 

It’s vital to drink plenty of water and replenish electrolytes during your intermittent fasting periods to avoid feeling lethargic and light-headed. 

To stay hydrated and promote balanced electrolyte levels, drink around eight cups of water daily, and add small amounts of sea salt, an excellent source of sodium and trace minerals, and a high-quality sugar-free electrolyte powder to your water. 

Watch the video below to learn how to stay hydrated while fasting.

Prolonged fasting

Prolonged fasting refers to fasting periods that are typically longer than 24 hours. 

Research published in PLOS One found that prolonged fasting enhances brain function, lowers the risk of age-related neurodegenerative diseases, increases human growth hormone levels and red blood cell count, and promotes a healthy body mass index.    

However, prolonged fasting without adequate fluid intake can cause hyper-concentrated urine and increases the risk of kidney stones. 

“I typically recommend drinking between two to three liters (8 to 12 cups) of water per day during prolonged fasts,” says Dr. Berg. “ Add one to two teaspoons of sea salt to your water, and don’t forget to include electrolytes to your fasting routine to maintain your energy levels, muscle functions, and mental focus.”

Fasting before medical procedures 

Fasting for a blood test or medical procedure isn’t the same as prolonged or intermittent fasting and may require you to abstain from food and drinks, including water.

While most fasting blood tests, such as a basic metabolic panel, permit water intake, other tests, such as a renal function panel or cholesterol test, may require you to limit or avoid water intake for 8 to 12 hours before the blood test. 

Surgeries or other medical procedures often require dry fasting to ensure that you have an empty stomach which lowers the risk of nausea, regurgitation, or vomiting.

It’s important to remember that different blood tests and medical procedures have different fasting protocols, and it's recommended to always check with your healthcare provider about specific guidelines for water intake. 

Dehydration illustration

Is it safe to do dry fasting?

Dry fasting is a form of fasting that involves abstaining from both food and water. Compared to water fasting, dry fasting has no additional metabolic benefits and may increase your risk of adverse health effects. 

Depriving the body of water for an extended period can result in severe dehydration, electrolyte imbalances, kidney problems, and nutritional deficiencies.

A study published in Sports Medicine found that a body water deficit of more than two percent can reduce blood flow to the brain and skeletal muscles, raise blood pressure, and may impair tissue oxygenation. 

Electrolyte powder in water

How much water should I drink while fasting?

How much water you should drink while fasting depends on your overall health, activity levels, climate, and the duration of your fast. 

If you practice intermittent fasting, it’s best to drink around eight cups (two liters) of water daily. Prolonged fasting periods may require 8 to 12 cups (two to three liters) of water daily to stay hydrated.

In addition, it’s crucial to replenish electrolytes with a high-quality, zero-calorie electrolyte powder (sugar-free) and support healthy sodium levels by adding one to two teaspoons of sea salt to your water throughout the day.   

Lemon water

Best drinks to have while fasting

Fasting involves limiting your caloric intake, but that doesn’t mean plain water is the only beverage you can drink.  

There are plenty of calorie-free drinks that you can enjoy during your fasting window:

  • Herbal tea 

  • Black and green tea 

  • Black coffee

  • Unsweetened flavored seltzer water

  • Sparkling water

  • Lemon water

In fact, lemons support healthy kidney function, and drinking lemon water is essential when fasting. Lemons are a rich source of citric acid, a natural acid that prevents oxalates from forming calcium oxalate crystals, the leading cause of kidney stones. 


Although not calorie-free, bulletproof coffee doesn’t break a fast and can help to extend your fasting periods. Bulletproof coffee is carb-free and won’t raise blood sugar and insulin levels, making it a popular drink for people on a keto diet and those that practice intermittent fasting.

Woman drinking water

Key takeaways

Can you drink water while fasting? Absolutely—drinking plenty of water while fasting is crucial to stay hydrated and support the normal functioning of your cells and tissues. 

It’s recommended to drink between 8 to 12 cups of water per day, replenish electrolytes and add sea salt to your water to avoid fasting-related fatigue, muscle cramps, and headaches. 


1. Is water allowed while doing intermittent fasting?

Water is allowed and recommended during intermittent fasting. Drinking around eight cups of water daily helps stay hydrated, lowers the risk of kidney stones, and supports the normal functioning of cells and tissues.  

2. Is it okay to drink water while fasting?

It’s vital to consume plenty of water while fasting to avoid dehydration, fatigue, kidney problems, and high blood pressure. 

Dry fasting doesn’t provide additional metabolic benefits to water fasting and can increase your risk of severe dehydration, electrolyte loss, impaired muscle function, and lack of tissue oxygenation.   

3. What liquids can you drink while fasting?

Zero-calorie drinks such as plain water, herbal teas, unsweetened flavored seltzer water, and lemon water are excellent choices for staying hydrated while fasting. 

Black coffee and green and black teas are also safe while fasting. However, it’s important to remember that these beverages contain caffeine, and it’s best to avoid large amounts to minimize caffeine’s side effects.  

4. Can I drink water before a blood test?

Yes, you can typically drink water before a blood test. In fact, it’s often recommended to stay well-hydrated before a blood test to ensure accurate results.

However, specific blood tests may require you to abstain from all foods and drinks, including water, and it’s best to check with your healthcare provider about water intake instructions before a blood test. 

5. What happens if you accidentally drink water while fasting for a blood test?

If you accidentally drink water before a blood test, it’s crucial to inform your doctor or phlebotomist. While most blood tests don’t require dry fasting, some specific blood tests may be less accurate if you consume water. 

6. Does fasting mean no water?

No, fasting doesn’t mean no water.

Fasting refers to limiting caloric intake by abstaining from food and calorie-containing beverages. Water has no calories and won’t interfere with your fast. In fact, drinking plenty of water is essential to avoid dehydration, fatigue, and muscle cramps while fasting.


7. Does lemon water break a fast?

Lemon water doesn’t break a fast and is an excellent choice to lower your risk of dehydration, hyper-concentrated urine, and kidney stones.  

Lemons contain citric acid, a natural acid that binds to oxalates and prevents the formation of calcium oxalate, the most common type of kidney stone.

8. Is it safe to fast without drinking water?

Dry fasting isn’t considered safe and can lead to severe dehydration, kidney stones, impaired tissue oxygenation and muscle functions, electrolyte imbalances, and nutrient deficiencies. 

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