Can you drink water while fasting for FBS?

January 12, 2026 •

3 min read

Medical experts confirm that drinking plain water is not only permissible but recommended when fasting for a blood test. This is because water contains no calories or sugars that could skew the results, unlike other beverages. Knowing if you can drink water while fasting for FBS is key to ensuring an accurate blood glucose reading.

Quick Summary

Drinking plain water is permitted and encouraged during the fasting period for a fasting blood sugar (FBS) test. It helps maintain hydration without affecting the test results, ensuring a more accurate reading and easier blood draw. Avoid all other foods and beverages.

Key Points

Plain Water is Allowed: Yes, you can drink plain, still, or sparkling water while fasting for an FBS test.
Stay Hydrated for Accuracy: Proper hydration prevents blood concentration and helps avoid falsely elevated blood sugar results.
Avoid All Other Beverages: Do not consume coffee, tea, juice, soda, milk, or flavored water, as they can interfere with test results.
Fasting Window is 8-12 Hours: Your fast should typically last 8 to 12 hours before the blood test.
Other Things to Avoid: For accurate results, also avoid chewing gum, smoking, and strenuous exercise.
Easier Blood Draw: Being well-hydrated makes it easier for the phlebotomist to draw your blood.
Check with Your Doctor: Always confirm specific fasting instructions with your healthcare provider, especially if you have diabetes or take regular medication.

Can You Drink Water While Fasting for FBS? The Definitive Answer

When preparing for a fasting blood sugar (FBS) test, a very common question arises: can I still drink water? The clear and definitive answer is yes. In fact, drinking plain water is not just allowed, but it is highly recommended during your fasting period. Water is a zero-calorie, zero-sugar fluid that will not interfere with the accuracy of your blood glucose test results. Staying adequately hydrated is crucial for a smooth and successful testing process.

Why You Must Drink Water During Your Fast

Your fasting period for an FBS test typically lasts 8 to 12 hours. Throughout this time, it is vital to stay hydrated. Dehydration can have a negative impact on your test results and the blood-drawing process. When you are dehydrated, your blood becomes more concentrated, which can lead to a falsely elevated blood sugar reading. By drinking plain water, you help maintain your body's normal fluid balance and prevent this from happening.

Furthermore, hydration can make the blood draw itself easier. When you are well-hydrated, your veins tend to be fuller and more visible. This makes it simpler for the phlebotomist to locate a vein and draw your blood, leading to a quicker and more comfortable experience for you. Drinking a glass or two of plain water before you leave for your appointment is a smart move.

What to Avoid During Your FBS Fast

While plain water is encouraged, it is equally important to know what liquids and foods are off-limits. Any beverage or food item that contains calories, sugar, or other substances can and will affect your blood glucose levels. To ensure the most accurate results, you must avoid the following during your 8- to 12-hour fast:

Coffee and tea (including black coffee and decaffeinated varieties)
Fruit juice and sodas (regular and diet)
Milk and milk products
Alcoholic beverages (avoid for at least 24 hours prior)
Chewing gum or mints (even sugar-free)
Any type of food or snack
Flavored or carbonated water with added sugars or artificial sweeteners

Even sugar-free beverages and gum can potentially stimulate your digestive system or contain chemicals that might influence test accuracy. Sticking exclusively to plain water is the safest and most reliable approach.

Fasting Instructions: A Quick Comparison


Item/Activity	Allowed During FBS Fast?	Reason	Action
Plain Water	Yes	Does not affect blood glucose levels; aids hydration.	Drink as needed.
Food (of any kind)	No	Food is broken down into glucose, which elevates blood sugar.	Stop eating 8-12 hours prior.
Coffee or Tea	No	Caffeine and other compounds can affect glucose levels; diuretics.	Skip your morning cup.
Sugar-Free Gum/Mints	No	Can trigger a digestive response and contain additives.	Avoid completely.
Strenuous Exercise	No	Intense activity can alter blood sugar levels.	Stick to light activities or rest.
Smoking	No	Can interfere with blood test results.	Avoid smoking before the test.

Maximizing Your Test Accuracy

For the most accurate FBS test results, follow these guidelines in the 24 hours leading up to your appointment:

Schedule your test early: An early morning appointment makes it easier to complete the fasting period overnight while you are sleeping.
Continue prescribed medications: Unless your doctor specifically tells you otherwise, continue taking any regular medications with plain water.
Inform your doctor of illness: Colds, fevers, or other illnesses can temporarily raise blood sugar. Let your doctor know if you are unwell, as the test may need to be rescheduled.
Maintain good hydration: Drink plenty of water throughout the days leading up to your fast to ensure you are well-hydrated, especially if you are prone to dizziness.

Conclusion

To summarize, when asked, "Can you drink water while fasting for FBS?" the answer is a resounding yes. Drinking plain, unflavored water is essential for maintaining proper hydration, which in turn helps ensure the accuracy of your blood sugar reading and makes the blood draw process smoother. Following the specific instructions from your healthcare provider regarding fasting duration and avoiding all other food and drink is crucial for reliable test results. By doing so, you can help your doctor get a clear and accurate picture of your blood glucose levels.

For more information on fasting for blood tests, you can consult reliable medical sources like MedlinePlus.

Frequently Asked Questions

No, you should not drink coffee, even black coffee or decaffeinated coffee, while fasting for an FBS test. Coffee contains compounds that can affect your blood sugar levels and act as a diuretic, potentially skewing your test results.

If you consume anything other than water during the fasting period, you must inform your doctor or the lab staff. They will likely advise you to reschedule the test to ensure the results are accurate.

No, flavored water is not permitted during a fast. It may contain sugars, artificial sweeteners, or other additives that can affect your blood glucose levels. Stick to plain, unflavored water.

While water doesn't actively lower blood sugar levels in the same way as medication, staying hydrated prevents dehydration from concentrating your blood. This helps ensure your reading is a true reflection of your fasting glucose and not inflated by dehydration.

You should continue to take your regular medication with plain water unless your doctor has specifically instructed you to do otherwise. Always follow your healthcare provider's directions.

No, you should not chew gum or have mints, including sugar-free varieties, while fasting. Chewing can stimulate digestion and some ingredients may affect your blood test results.

The standard fasting period is typically 8 to 12 hours before your blood is drawn. Your doctor will provide you with the exact timeframe required for your test.

A fasting blood test is necessary because it measures your baseline blood glucose levels when they are not affected by food or drink. This provides the most accurate snapshot of your body's ability to regulate blood sugar, aiding in the diagnosis of conditions like prediabetes or diabetes.