Can you drink water while intermittent fasting?

Yes. Water has no calories and does not break a fast. You should drink it throughout.

Why do I get a headache when fasting?

Often it is mild dehydration, sometimes less caffeine than usual or low salt. Drinking water is the first thing to try. If headaches are severe or persistent, stop and see a doctor.

Do coffee and tea count towards water intake?

They do contribute fluid. Plain water should still make up most of what you drink.

How much water should you drink while fasting?

A little more than you think, spread through the day. Here is a practical target and how to hit it.

Short answer

A good starting target is about 2 litres (roughly 8 glasses) of water a day while intermittent fasting, and more if you are active, large, or in hot weather. Spread it through the day and drink whenever you feel thirsty or hungry during the fast.

A practical daily target

There is no single correct number. Around 2 litres is a sensible default for most adults. You need more if you exercise, sweat a lot, drink a lot of coffee, or live somewhere hot. Pale yellow urine is a simple sign you are drinking enough.

Why you need to drink more when fasting

A fair share of daily water normally comes from food. During a fast that source is gone.
In the first days of fasting the body tends to release more water and salt.
Thirst and hunger are easy to confuse. Drinking first often makes the hunger pass.

Signs you need more water

Headache, especially late in the fast
Tiredness or trouble concentrating
Dry mouth or dark urine
Feeling light-headed when you stand up

If you feel dizzy, confused or unwell and water does not help, end the fast and eat. Seek medical advice if symptoms continue.

Simple ways to drink enough

Have a large glass when you wake up.
Keep a bottle where you can see it.
Drink a glass each time hunger shows up during the fast.
Sparkling water or plain tea count if you are bored of still water. See what you can drink while fasting.

Hit your water goal with Bide

Bide tracks water next to your fast, so you see both in one glance.

Start with your daily goal
Bide sets a daily water goal during setup. The water card shows how far along you are.
Log each drink in one tap
Use +250 ml or +500 ml, pick a glass, cup, mug or bottle, or type an amount.
Review the day
Open the water log to see when you drank. It resets each day, so every morning starts at zero.

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Common questions

Yes. Water has no calories and does not break a fast. You should drink it throughout.

Sources

The studies and health guidance this guide draws on.

Water, drinks and hydrationNHS
Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and SulfateNational Academies Press, 2005
No Evidence of Dehydration with Moderate Daily Coffee Intake: A Counterbalanced Cross-Over Study in a Free-Living PopulationPLOS ONE, 2014

This guide is general information, not medical advice. Talk to a doctor before fasting if you are pregnant or breastfeeding, under 18, have a health condition or take medication.

Short answer

A practical daily target

Why you need to drink more when fasting

Signs you need more water

Simple ways to drink enough

Hit your water goal with Bide

Start with your daily goal

Log each drink in one tap

Review the day

Common questions

Sources

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